1
|
Remodeling of Cardiac Gap Junctional Cell-Cell Coupling. Cells 2021; 10:cells10092422. [PMID: 34572071 PMCID: PMC8465208 DOI: 10.3390/cells10092422] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2021] [Revised: 09/03/2021] [Accepted: 09/08/2021] [Indexed: 12/29/2022] Open
Abstract
The heart works as a functional syncytium, which is realized via cell-cell coupling maintained by gap junction channels. These channels connect two adjacent cells, so that action potentials can be transferred. Each cell contributes a hexameric hemichannel (=connexon), formed by protein subuntis named connexins. These hemichannels dock to each other and form the gap junction channel. This channel works as a low ohmic resistor also allowing the passage of small molecules up to 1000 Dalton. Connexins are a protein family comprising of 21 isoforms in humans. In the heart, the main isoforms are Cx43 (the 43 kDa connexin; ubiquitous), Cx40 (mostly in atrium and specific conduction system), and Cx45 (in early developmental states, in the conduction system, and between fibroblasts and cardiomyocytes). These gap junction channels are mainly located at the polar region of the cardiomyocytes and thus contribute to the anisotropic pattern of cardiac electrical conductivity. While in the beginning the cell–cell coupling was considered to be static, similar to an anatomically defined structure, we have learned in the past decades that gap junctions are also subject to cardiac remodeling processes in cardiac disease such as atrial fibrillation, myocardial infarction, or cardiomyopathy. The underlying remodeling processes include the modulation of connexin expression by e.g., angiotensin, endothelin, or catecholamines, as well as the modulation of the localization of the gap junctions e.g., by the direction and strength of local mechanical forces. A reduction in connexin expression can result in a reduced conduction velocity. The alteration of gap junction localization has been shown to result in altered pathways of conduction and altered anisotropy. In particular, it can produce or contribute to non-uniformity of anisotropy, and thereby can pre-form an arrhythmogenic substrate. Interestingly, these remodeling processes seem to be susceptible to certain pharmacological treatment.
Collapse
|
2
|
Valiunas V, Cohen IS, Brink PR. Defining the factors that affect solute permeation of gap junction channels. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2018; 1860:96-101. [PMID: 28690048 PMCID: PMC5705451 DOI: 10.1016/j.bbamem.2017.07.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 06/30/2017] [Accepted: 07/03/2017] [Indexed: 01/22/2023]
Abstract
This review focuses on the biophysical properties and structure of the pore and vestibule of homotypic gap junction channels as they relate to channel permeability and selectivity. Gap junction channels are unique in their sole role to connect the cytoplasm of two adjacent cells. In general, these channels are considered to be poorly selective, possess open probabilities approximating unity, and exhibit mean open times ranging from milliseconds to seconds. These properties suggest that such channels can function as delivery pathways from cell to cell for solutes that are significantly larger than monovalent ions. We have taken quantitative data from published works concerning unitary conductance, ion flux, and permeability for homotypic connexin 43 (Cx43), Cx40, Cx26, Cx50, and Cx37, and performed a comparative analysis of conductance and/or ion/solute flux versus diffusion coefficient. The analysis of monovalent cation flux portrays the pore as equivalent to an aqueous space where hydrogen bonding and weak interactions with binding sites dominate. For larger solutes, size, shape and charge are also significant components in determining the permeation rate. This article is part of a Special Issue entitled: Gap Junction Proteins edited by Jean Claude Herve.
Collapse
Affiliation(s)
- Virginijus Valiunas
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA.
| | - Ira S Cohen
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA
| | - Peter R Brink
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA.
| |
Collapse
|
3
|
Wang HZ, Rosati B, Gordon C, Valiunas V, McKinnon D, Cohen IS, Brink PR. Inhibition of histone deacetylase (HDAC) by 4-phenylbutyrate results in increased junctional conductance between rat corpora smooth muscle cells. Front Pharmacol 2015; 6:9. [PMID: 25691868 PMCID: PMC4315027 DOI: 10.3389/fphar.2015.00009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 01/11/2015] [Indexed: 01/02/2023] Open
Abstract
4-phenylbutyrate (4-PB) has been shown to increase the protein content in a number of cells types. One such protein is Connexin43 (Cx43). We show here that 4-phenylbutyrate exposure results in significantly elevated cell to cell coupling, as determined by dual whole cell patch clamp. Incubation with 5 mM 4PB for 24 h or more nearly doubles junctional conductance. Interestingly, mRNA levels for Cx43 declined with exposure to 4-PB while western blot analysis revealed not significant change in protein levels. These data are most consistent with stabilization of the existing Cx43 pool or alterations in the number of functional channels within an existing pool of active and silent channels. These data represent a baseline for testing the efficacy of increased connexin mediated coupling in a variety of multicellular functions including erectile function.
Collapse
Affiliation(s)
- Hong Zhan Wang
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA
| | - Barbara Rosati
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA ; Department of Physiology and Biophysics, Molecular Cardiology Institute, Stony Brook University Stony Brook, NY, USA
| | - Chris Gordon
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA
| | - Virginijus Valiunas
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA ; Department of Physiology and Biophysics, Molecular Cardiology Institute, Stony Brook University Stony Brook, NY, USA
| | - David McKinnon
- Department of Physiology and Biophysics, Molecular Cardiology Institute, Stony Brook University Stony Brook, NY, USA ; Department of Neurobiology and Behavior, Stony Brook University Stony Brook, NY, USA
| | - Ira S Cohen
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA ; Department of Physiology and Biophysics, Molecular Cardiology Institute, Stony Brook University Stony Brook, NY, USA
| | - Peter R Brink
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA ; Department of Physiology and Biophysics, Molecular Cardiology Institute, Stony Brook University Stony Brook, NY, USA
| |
Collapse
|
4
|
Valiunas V, Wang HZ, Li L, Gordon C, Valiuniene L, Cohen IS, Brink PR. A comparison of two cellular delivery mechanisms for small interfering RNA. Physiol Rep 2015; 3:3/2/e12286. [PMID: 25649248 PMCID: PMC4393195 DOI: 10.14814/phy2.12286] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Cellular delivery of small interfering RNAs to target cells of a tissue has the potential to travel by two intercellular pathways. For intimately apposed cells gap junctions allow transport exclusive of the extracellular space. For cells not in intimate contact, exocytotic release of vesicular contents and subsequent retrieval via endocytosis of exosomes and other vesicular contents represent an alternative intercellular delivery system that utilizes the extracellular space. Previous studies have shown siRNA/miRNA transfer from a delivery cell to a target cell via gap junction channels. We hypothesized that siRNA can be delivered via gap junctions and downregulate the expression of a reporter gene, the cyclic nucleotide-gated cation channel gene (mHCN2), in the recipient cells of cell pairs. Whole-cell patch clamp was used to measure the mHCN2-induced current and junctional conductance. The target cells were HEK293 cells that endogenously express Cx43 or HeLaCx43 cells, both transfected with mHCN2. The source cells were HEK293 or HeLaCx43 cells transfected with fluorescent-labeled siRNA targeting mHCN2. We found that siRNA targeting mHCN2 resulted in significant downregulation of mHCN2 currents both in single cells and the recipient cell of a cell pair. In addition we also documented downregulation in target cells that were not in contact with source cells suggesting an extracellular-mediated delivery. To test further for extracellular delivery HEK293/HCN2 or HeLaCx43/HCN2 cells were cultured in medium collected from HEK293 or HeLaCx43 cells transfected with fluorescent-labeled siRNA or fluorescent-labeled morpholino designed to target HCN2. After 24 h single HEK293/HCN2 or HeLaCx43cells showed accumulation of siRNA. The mHCN2 currents were also down regulated in cells with siRNA uptake. Application of 200 nmol/L Bafilomycin A1, which has been shown to affect endosome acidification and endocytotic activity, resulted in a smaller accumulation of fluorescent-labeled siRNA in single target cells. In distinction to siRNA, morpholinos targeting HCN2 exhibited greatly reduced extracellularly mediated transfer while in cell pairs, target cells exhibited reduced HCN2 currents consistent with effective gap junction-mediated delivery.
Collapse
Affiliation(s)
- Virginijus Valiunas
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Hong-Zhang Wang
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Ling Li
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Chris Gordon
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Laima Valiuniene
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Ira S Cohen
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| | - Peter R Brink
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, New York
| |
Collapse
|
5
|
Christ GJ. The Control of Corporal Smooth Muscle Tone, the Coordination of Penile Erection, and the Etiology of Erectile Dysfunction: The Devil is in the Details. ACTA ACUST UNITED AC 2015. [DOI: 10.1080/01614576.1998.11074239] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
6
|
Sung HH, Choo SH, Han DH, Chae MR, Kang SJ, Park CS, So I, Park JK, Lee SW. Effect of the novel BKCa channel opener LDD175 on the modulation of corporal smooth muscle tone. J Sex Med 2014; 12:29-38. [PMID: 25385091 DOI: 10.1111/jsm.12744] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
INTRODUCTION The BKCa channel has been reported to play an important role in erectile function. Recently, novel BKCa channel activator, LDD175, was introduced. AIM This study aims to investigate whether LDD175 relaxes corporal smooth muscle (CSM) via BKCa channel activation. METHODS After isolation of CSM strip from a male rabbit model, contraction studies using organ bath was performed. Isolating human tissue and cell cultures, electrophysiological studies were done via whole-cell patch-clamp recording. MAIN OUTCOME MEASURES Vasodilatory effects of LDD175 were evaluated by cumulative addition ranging from 10(-7) to 10(-4) M in corpus cavernosal strips after precontraction with 10(-5) M phenylephrine via organ bath system. Using cultured human CSM cells, patch-clamp recording was performed. Erectile function was measured by in vivo rat cavernous nerve stimulation. RESULTS LDD175 caused an endothelium-independent relaxation of corporal tissues, and this effect was abolished by pretreatment with iberiotoxin. The relaxation effect of 10(-4) M LDD175 was greater than that of 10(-6) M udenafil (54.0 ± 3.1% vs. 34.5 ± 3.9%, P < 0.05); 10(-5) M LDD175 with 10(-6) M udenafil caused a greater relaxation effect on strips than 10(-5) M LDD175 or 10(-6) M udenafil alone (50.7%, 34.1%, vs. 20.7%, respectively, P < 0.001). In patch-clamp recordings, LDD175 increased K(+) currents in a dose-dependent manner, and washout of LDD175 or the addition of iberiotoxin fully reversed the increase. Intravenous LDD175 improved erectile function measured by area under the curve (AUC) of the intracavernosal pressure (ICP)/arterial blood pressure (ABP) ratio (1,612.1 ± 135.6 vs. 1,093.7 ± 123.1, P < 0.05). There was no difference between 10 mg/kg LDD175 and 1 mg/kg udenafil regarding maximal ICP, maximal ICP/ABP ratio, and the AUC of the ICP/ABP ratio (P > 0.05). CONCLUSIONS LDD175 leads to an endothelium-independent relaxation of erectile tissue, primarily through the opening of BKCa channels. The results suggest that LDD175 might be a new candidate treatment for erectile dysfunction.
Collapse
Affiliation(s)
- Hyun Hwan Sung
- The Department of Urology, Samsung Medical Center, Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Seoul, Korea
| | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Thévenin AF, Kowal TJ, Fong JT, Kells RM, Fisher CG, Falk MM. Proteins and mechanisms regulating gap-junction assembly, internalization, and degradation. Physiology (Bethesda) 2014; 28:93-116. [PMID: 23455769 DOI: 10.1152/physiol.00038.2012] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Gap junctions (GJs) are the only known cellular structures that allow a direct cell-to-cell transfer of signaling molecules by forming densely packed arrays or "plaques" of hydrophilic channels that bridge the apposing membranes of neighboring cells. The crucial role of GJ-mediated intercellular communication (GJIC) for all aspects of multicellular life, including coordination of development, tissue function, and cell homeostasis, has been well documented. Assembly and degradation of these membrane channels is a complex process that includes biosynthesis of the connexin (Cx) subunit proteins (innexins in invertebrates) on endoplasmic reticulum (ER) membranes, oligomerization of compatible subunits into hexameric hemichannels (connexons), delivery of the connexons to the plasma membrane (PM), head-on docking of compatible connexons in the extracellular space at distinct locations, arrangement of channels into dynamic spatially and temporally organized GJ channel plaques, as well as internalization of GJs into the cytoplasm followed by their degradation. Clearly, precise modulation of GJIC, biosynthesis, and degradation are crucial for accurate function, and much research currently addresses how these fundamental processes are regulated. Here, we review posttranslational protein modifications (e.g., phosphorylation and ubiquitination) and the binding of protein partners (e.g., the scaffolding protein ZO-1) known to regulate GJ biosynthesis, internalization, and degradation. We also look closely at the atomic resolution structure of a GJ channel, since the structure harbors vital cues relevant to GJ biosynthesis and turnover.
Collapse
Affiliation(s)
- Anastasia F Thévenin
- Department of Biological Sciences, Lehigh University, Bethlehem, Pennsylvania, USA
| | | | | | | | | | | |
Collapse
|
8
|
Kaufman J, Gordon C, Bergamaschi R, Wang HZ, Cohen IS, Valiunas V, Brink PR. The effects of the histone deacetylase inhibitor 4-phenylbutyrate on gap junction conductance and permeability. Front Pharmacol 2013; 4:111. [PMID: 24027526 PMCID: PMC3759747 DOI: 10.3389/fphar.2013.00111] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 08/14/2013] [Indexed: 11/20/2022] Open
Abstract
Longitudinal resistance is a key factor in determining cardiac action potential propagation. Action potential conduction velocity has been shown to be proportional to the square root of longitudinal resistance. A major determinant of longitudinal resistance in myocardium is the gap junction channel, comprised connexin proteins. Within the ventricular myocardium connexin43 (Cx43) is the dominantly expressed connexin. Reduced numbers of gap junction channels will result in an increase in longitudinal resistance creating the possibility of slowed conduction velocity while increased numbers of channels would potentially result in an increase in conduction velocity. We sought to determine if inhibition of histone deacetylase (HDAC) by 4-phenylbutyrate (4-PB), a known inhibitor of HDAC resulted in an increase in junctional conductance and permeability, which is not the result of changes in single channel unitary conductance. These experiments were performed using HEK-293 cells and HeLa cells stably transfected with Cx43. Following treatment with increasing concentrations of 4-PB up-regulation of Cx43 was observed via Western blot analysis. Junctional (gj) conductance and unitary single channel conductance were measured via whole-cell patch clamp. In addition intercellular transfer of lucifer yellow (LY) was determined by fluorescence microscopy. The data in this study indicate that 4-PB is able to enhance functional Cx43 gap junction coupling as indicated by LY dye transfer and multichannel and single channel data along with Western blot analysis. As a corollary, pharmacological agents such as 4-PB have the potential, by increasing intercellular coupling, to reduce the effect of ischemia. It remains to be seen whether drugs like 4-PB will be effective in preventing cardiac maladies.
Collapse
Affiliation(s)
- Joshua Kaufman
- Department of Physiology and Biophysics, Stony Brook University Stony Brook, NY, USA
| | | | | | | | | | | | | |
Collapse
|
9
|
Brink PR, Valiunas V, Gordon C, Rosen MR, Cohen IS. Can gap junctions deliver? BIOCHIMICA ET BIOPHYSICA ACTA 2012; 1818:2076-81. [PMID: 21986484 DOI: 10.1016/j.bbamem.2011.09.025] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Revised: 09/09/2011] [Accepted: 09/23/2011] [Indexed: 01/08/2023]
Abstract
In vivo delivery of small interfering RNAs (siRNAs) to target cells via the extracellular space has been hampered by dilution effects and immune responses. Gap junction-mediated transfer between cells avoids the extracellular space and its associated limitations. Because of these advantages cell based delivery via gap junctions has emerged as a viable alternative for siRNA or miRNA delivery. Here we discuss the advantages and disadvantages of extracellular delivery and cell to cell delivery via gap junction channels composed of connexins. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.
Collapse
Affiliation(s)
- Peter R Brink
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, USA.
| | | | | | | | | |
Collapse
|
10
|
Effects of ginsenoside on large-conductance KCa channels in human corporal smooth muscle cells. Int J Impot Res 2011; 23:193-9. [DOI: 10.1038/ijir.2011.25] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
11
|
Spray DC, Suadicani SO, Srinivas M, Gutstein DE, Fishman GI. Gap Junctions in the Cardiovascular System. Compr Physiol 2011. [DOI: 10.1002/cphy.cp020104] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
12
|
Kanaporis G, Brink PR, Valiunas V. Gap junction permeability: selectivity for anionic and cationic probes. Am J Physiol Cell Physiol 2010; 300:C600-9. [PMID: 21148413 DOI: 10.1152/ajpcell.00316.2010] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Gap junction channels formed by different connexins exhibit specific permeability to a variety of larger solutes including second messengers, polypeptides, and small interfering RNAs. Here, we report the permeability of homotypic connexin26 (Cx26), Cx40, Cx43, and Cx45 gap junction channels stably expressed in HeLa cells to solutes with different size and net charge. Channel permeability was determined using simultaneous measurements of junctional conductance and the cell-cell flux of a fluorescent probe. All four connexins allowed passage of both cationic and anionic probes, but the transfer rates were connexin dependent. The negatively charged probes [Lucifer yellow (LY; median axial diameter 9.9 Å, charge -2), carboxyfluorescein (CF; 8.2 Å; -2), and Alexa Fluor350 (AF350, 5.4 Å; -1)] exhibited the following permeability order: Cx43 > Cx45 > Cx26 > Cx40. In contrast, for the positively charged species permeability, the orders were as follows: Cx26 ≈ Cx43 ≈ Cx40 ≈ Cx45 for N,N,N-trimethyl-2-[methyl-(7-nitro-2,1,3-benzoxadiol-4-yl) amino] ethanaminium (NBD-m-TMA; 5.5 Å, +1) and Cx26 ≥ Cx43 ≈ Cx40 > Cx45 for ethidium bromide (10.3 Å, +1). Comparison of probe permeability relative to K(+) revealed that Cx43 and Cx45 exhibited similar permeability for NBD-m-TMA and AF350, indicating weak charge selectivity. However, lesser transfer of CF and LY through Cx45 relative to Cx43 channels suggests stronger size-dependent discrimination of solute. The permeability of NBD-m-TMA for Cx40 and Cx26 channels was approximately three times higher than to anionic AF350 despite the fact that both have similar minor diameters, suggesting charge selectivity. In conclusion, these results confirm that channels formed from individual connexins can discriminate for solutes based on size and charge, suggesting that channel selectivity may be a key factor in cell signaling.
Collapse
Affiliation(s)
- G Kanaporis
- Dept. of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794-8661, USA
| | | | | |
Collapse
|
13
|
Jung JH, Kim BJ, Chae MR, Kam SC, Jeon JH, So I, Chung KH, Lee SW. Gene Transfer of TRPC6DN (Dominant Negative) Restores Erectile Function in Diabetic Rats. J Sex Med 2010; 7:1126-38. [PMID: 20059667 DOI: 10.1111/j.1743-6109.2009.01634.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
14
|
Kanaporis G, Mese G, Valiuniene L, White TW, Brink PR, Valiunas V. Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides. J Gen Physiol 2008; 131:293-305. [PMID: 18378798 PMCID: PMC2279171 DOI: 10.1085/jgp.200709934] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2007] [Accepted: 03/05/2008] [Indexed: 11/30/2022] Open
Abstract
Gap junction channels exhibit connexin dependent biophysical properties, including selective intercellular passage of larger solutes, such as second messengers and siRNA. Here, we report the determination of cyclic nucleotide (cAMP) permeability through gap junction channels composed of Cx43, Cx40, or Cx26 using simultaneous measurements of junctional conductance and intercellular transfer of cAMP. For cAMP detection the recipient cells were transfected with a reporter gene, the cyclic nucleotide-modulated channel from sea urchin sperm (SpIH). cAMP was introduced via patch pipette into the cell of the pair that did not express SpIH. SpIH-derived currents (I(h)) were recorded from the other cell of a pair that expressed SpIH. cAMP diffusion through gap junction channels to the neighboring SpIH-transfected cell resulted in a five to sixfold increase in I(h) current over time. Cyclic AMP transfer was observed for homotypic Cx43 channels over a wide range of conductances. However, homotypic Cx40 and homotypic Cx26 exhibited reduced cAMP permeability in comparison to Cx43. The cAMP/K(+) permeability ratios were 0.18, 0.027, and 0.018 for Cx43, Cx26, and Cx40, respectively. Cx43 channels were approximately 10 to 7 times more permeable to cAMP than Cx40 or Cx26 (Cx43 > Cx26 > or = Cx40), suggesting that these channels have distinctly different selectivity for negatively charged larger solutes involved in metabolic/biochemical coupling. These data suggest that Cx43 permeability to cAMP results in a rapid delivery of cAMP from cell to cell in sufficient quantity before degradation by phosphodiesterase to trigger relevant intracellular responses. The data also suggest that the reduced permeability of Cx26 and Cx40 might compromise their ability to deliver cAMP rapidly enough to cause functional changes in a recipient cell.
Collapse
Affiliation(s)
- Giedrius Kanaporis
- Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY 11794, USA
| | | | | | | | | | | |
Collapse
|
15
|
Mathias RT, White TW, Brink PR. Chapter 3 The Role of Gap Junction Channels in the Ciliary Body Secretory Epithelium. CURRENT TOPICS IN MEMBRANES 2008. [DOI: 10.1016/s1063-5823(08)00403-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
16
|
So I, Chae MR, Lee SW. Gene transfer of the K(ATP) channel restores age-related erectile dysfunction in rats. BJU Int 2007; 100:1154-60. [PMID: 17645416 DOI: 10.1111/j.1464-410x.2007.07050.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVE To determine if gene transfer of the ATP-sensitive potassium (K(ATP)) channel can reverse age-related erectile dysfunction in the rat, as the K(ATP) channel is an important subtype of potassium channels regulating smooth muscle tone. MATERIALS AND METHODS In an in vitro study, gene were transferred using cDNA of the K(ATP) channel in cultured human corporal smooth muscle (CSM) cells and human embryonic kidney (HEK) cells. After gene transfer, the activities of transferred channels were assessed by the patch-clamp technique. In an in vivo study, 15 old rats were used for groups of gene therapy and nine young adult rats were used as normal controls. The old rats were divided into three groups, i.e. controls and two gene-transfer groups (Kir6.1 + SUR2B and Kir6.2 + SUR2B). The intracavernosal pressure (ICP) response to cavernosal nerve stimulation was assessed after intracorporal injection with naked cDNA of the K(ATP) channel. The transgene expression of the K(ATP) channel was examined by reverse transcription-polymerase chain reaction (RT-PCR) in rats transfected with cDNA of Kir 6.1 and 6.2. RESULTS The transferred gene of the K(ATP) channel was functionally active and appropriate for gene transfer. The mean (sem) ratio of ICP to systemic blood pressure in the gene-transfer groups, at 79.4 (1)% and 76.5 (2.6)% (both eight rats) was significantly higher than that in age-matched control rats, at 59.4 (3.3)% (eight), and similar to that in the young control rats, at 77.1 (2.7)% (nine). The RT-PCR showed expression of Kir6.1 and 6.2 genes in the transfected groups. CONCLUSION In vivo gene transfer of the K(ATP) channel can physiologically restore erectile function in aged rats, and might be applicable to the development of new forms of therapy for treating human erectile dysfunction.
Collapse
Affiliation(s)
- Insuk So
- Department of Urology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul National University College of Medicine, Seoul, Korea
| | | | | |
Collapse
|
17
|
Wang HZ, Brink PR, Christ GJ. Gap junction channel activity in short-term cultured human detrusor myocyte cell pairs: gating and unitary conductances. Am J Physiol Cell Physiol 2006; 291:C1366-76. [PMID: 16899553 DOI: 10.1152/ajpcell.00027.2006] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Several independent lines of investigation indicate that intercellular communication through gap junctions modulates bladder physiology and, moreover, that altered junctional communication may contribute to detrusor overactivity. However, as far as we are aware, there are still no direct recordings of gap junction-mediated intercellular currents between human or rat detrusor myocytes. Northern and Western blots were used to identify connexin expression in frozen human bladder tissue and short-term cultured human detrusor myocytes. Double whole cell patch (DWCP) recording revealed that human detrusor myocyte cell pairs were well coupled with an average junctional conductance of 6.5 ± 4.6 nS (ranging from 0.1 to 15 nS, n = 22 cell pairs). Macroscopic gap junction channel currents in human detrusor myocytes exhibited voltage dependence similar to homotypic connexin43. The normalized transjunctional conductance-voltage ( Gj- Vj) relationship was symmetrical and well described by a two-state Boltzmann relation ( Gmin≈ 0.33, V0= 63.6 mV, Z = 0.117 or equal to 2.95 gating charges), suggestive of a bilateral voltage-gated mechanism. In symmetric 165 mM CsCl, the measured single-channel slope conductance was ∼120 pS for the fully open channel and ∼26 pS for the major substate. Occasionally, other subconductance states were also observed. The single-channel mean open time declined with increasing Vj, accounting for the Vj-dependent decline of macroscopic junctional current. Qualitatively similar electrophysiological characteristics were observed in DWCP of freshly isolated rat detrusor myocytes. These data confirm and extend previous observations and are consistent with reports in other smooth muscle cells types in which Cx43-mediated intercellular communication has been identified.
Collapse
Affiliation(s)
- H-Z Wang
- Department of Urology, Albert Einstein College of Medicine, Bronx
| | | | | |
Collapse
|
18
|
Zhang Q, Cao C, Mangano M, Zhang Z, Silldorff EP, Lee-Kwon W, Payne K, Pallone TL. Descending vasa recta endothelium is an electrical syncytium. Am J Physiol Regul Integr Comp Physiol 2006; 291:R1688-99. [PMID: 16840652 DOI: 10.1152/ajpregu.00261.2006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We examined gap junction coupling of descending vasa recta (DVR). DVR endothelial cells or pericytes were depolarized to record the associated capacitance transients. Virtually all endothelia and some pericytes exhibited prolonged transients lasting 10-30 ms. Carbenoxolone (100 microM) and 18beta-glycyrrhetinic acid (18betaGRA; 100 microM) markedly shortened the endothelial transients. Carbenoxolone and heptanol (2 mM) reduced the pericyte capacitance transients when they were prolonged. Lucifer yellow (LY; 2 mM) was dialyzed into the cytoplasm of endothelial cells and pericytes. LY spread diffusely along the endothelial monolayer, whereas in most pericytes, it was confined to a single cell. In some pericytes, complex patterns of LY spreading were observed. DVR cells were depolarized by voltage clamp as fluorescence of bis(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)] was monitored approximately 200 microm away. A 40-mV endothelial depolarization was accompanied by a 26.1 +/- 5.5-mV change in DiBAC(4)(3) fluorescence. DiBAC(4)(3) fluorescence did not change after 18betaGRA or when pericytes were depolarized. Similarly, propagated cytoplasmic Ca(2+) responses arising from mechanical perturbation of the DVR wall were attenuated by 18betaGRA or heptanol. Connexin (Cx) immunostaining showed predominant linear Cx40 and Cx43 in endothelia, whereas Cx37 stained smooth muscle actin-positive pericytes. We conclude that the DVR endothelium is an electrical syncytium and that gap junction coupling in DVR pericytes exists but is less pronounced.
Collapse
Affiliation(s)
- Qingli Zhang
- Division of Nephrology N3W143, University of Maryland School of Medicine, 22 S. Greene Street, Baltimore, MD 21201, USA
| | | | | | | | | | | | | | | |
Collapse
|
19
|
Brink PR, Valiunas V, Wang HZ, Zhao W, Davies K, Christ GJ. Experimental diabetes alters connexin43 derived gap junction permeability in short-term cultures of rat corporeal vascular smooth muscle cells. J Urol 2006; 175:381-6. [PMID: 16406945 DOI: 10.1016/s0022-5347(05)00007-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Indexed: 10/25/2022]
Abstract
PURPOSE Intercellular communication through gap junctions was assessed in 8 to 10-week STZ diabetic rats to evaluate diabetes related effects on gap junctional conductance and permeability in short-term cultures of corporeal myocytes. MATERIALS AND METHODS Rats were made diabetic by a single intraperitoneal injection of STZ. Eight to 10 weeks later erectile function was evaluated in vivo and corporeal tissue was harvested to isolate corporeal myocytes. Dual whole cell patch clamp studies of intercellular communication through connexin43 (Cx43) derived gap junction channels were done in short-term, ie passages 0 to 2, cultured corporeal myocytes excised from STZ diabetic rats with documented erectile impairment as well as in myocytes from age matched control rats. RESULTS No differences in macroscopic junctional conductance, single channel conductance or open probability were detected between myocytes from age matched control and STZ diabetic rats, confirming the lack of diabetes related alterations in Cx43 gating or conductance. However, fluorescence dye transfer experiments revealed a marked 3-fold increase in Cx43 mediated junctional permeability in the absence of any detectable change in Cx43 protein expression. CONCLUSIONS These data suggest that an alteration in the selectivity filter of Cx43 in diabetic animals affects the permeability of specifically sized and charged solutes. To our knowledge these studies provide the first evidence of a diabetes related increase in intercellular permselectivity in corporeal myocytes and, thus, they may have important implications for diabetes related erectile dysfunction.
Collapse
Affiliation(s)
- Peter R Brink
- Department of Physiology and Biophysics and Institute for Molecular Cardiology, State University of New York at Stony Brook, Stony Brook, USA.
| | | | | | | | | | | |
Collapse
|
20
|
Hassan GS, Mukherjee S, Nagajyothi F, Weiss LM, Petkova SB, de Almeida CJ, Huang H, Desruisseaux MS, Bouzahzah B, Pestell RG, Albanese C, Christ GJ, Lisanti MP, Tanowitz HB. Trypanosoma cruzi infection induces proliferation of vascular smooth muscle cells. Infect Immun 2006; 74:152-9. [PMID: 16368968 PMCID: PMC1346667 DOI: 10.1128/iai.74.1.152-159.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Trypanosoma cruzi infection causes cardiomyopathy and vasculopathy. Previous studies have demonstrated that infection of human umbilical vein endothelial and smooth muscle cells resulted in activation of extracellular signal-regulated kinase (ERK). In the present study, smooth muscle cells were infected with trypomastigotes, and immunoblot analysis revealed an increase in the expression of cyclin D1 and proliferating cell nuclear antigen (PCNA), important mediators of smooth muscle cell proliferation. Interestingly, after infection, the expression of caveolin-1 was reduced in both human umbilical vein endothelial cells and smooth muscle cells. Immunoblot and immunohistochemical analyses of lysates of carotid arteries obtained from infected mice revealed increased expression of PCNA, cyclin D1, its substrate, phospho-Rb (Ser780), and phospho-ERK1/2. The expression of the cyclin-dependent kinase inhibitor p21(Cip1/Waf1), caveolin-1, and caveolin-3 was reduced in carotid arteries obtained from infected mice. There was an increase in the abundance of pre-pro-endothelin-1 mRNA in the carotid artery and aorta from infected mice. The ET(A) receptor was also elevated in infected arteries. ERK activates endothelin-1, which in turn exerts positive feedback activating ERK, and cyclin D1 is a downstream target of both endothelin-1 and ERK. There was significant incorporation of bromodeoxyuridine into smooth muscle cell DNA when treatment was with conditioned medium obtained from infected endothelial cells. Taken together, these data suggest that T. cruzi infection stimulates smooth muscle cell proliferation and is likely a result of the upregulation of the ERK-cyclin D1-endothelin-1 pathway.
Collapse
MESH Headings
- Animals
- Bromodeoxyuridine/metabolism
- Carotid Arteries/enzymology
- Caveolins/biosynthesis
- Caveolins/genetics
- Cell Cycle/physiology
- Cell Proliferation
- Cells, Cultured
- Chagas Disease/metabolism
- Chagas Disease/pathology
- Cyclin D1/physiology
- Endothelial Cells/metabolism
- Endothelial Cells/parasitology
- Endothelin-1/genetics
- Extracellular Signal-Regulated MAP Kinases/physiology
- Humans
- Male
- Mice
- Mice, Inbred A
- Mice, Inbred C3H
- Muscle, Smooth, Vascular/parasitology
- Muscle, Smooth, Vascular/pathology
- Myocytes, Smooth Muscle/parasitology
- Myocytes, Smooth Muscle/pathology
- Proliferating Cell Nuclear Antigen/physiology
- RNA Precursors/metabolism
- Receptor, Endothelin A/metabolism
- Trypanosoma cruzi/physiology
Collapse
Affiliation(s)
- Ghada S Hassan
- Department of Pathology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461, USA
| | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
21
|
Experimental Diabetes Alters Connexin43 Derived Gap Junction Permeability in Short-Term Cultures of Rat Corporeal Vascular Smooth Muscle Cells. J Urol 2006. [DOI: 10.1097/00005392-200601000-00124] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
22
|
Szigeti GP, Somogyi GT, Csernoch L, Széll EA. Age-dependence of the spontaneous activity of the rat urinary bladder. J Muscle Res Cell Motil 2005; 26:23-9. [PMID: 16025204 DOI: 10.1007/s10974-005-9003-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2005] [Revised: 06/10/2005] [Accepted: 06/17/2005] [Indexed: 11/28/2022]
Abstract
Abnormal mechanical function of the bladder is manifested in a number of ways including higher frequency of involuntary detrusor contractions associated with reduced compliance of the bladder that is responsible for an increase in intraluminal pressure during filling. There are basically two ways to approach experimentally these problems: (1) by studying the neural control of the lower urinary tract function, and (2) by measuring the properties of smooth muscle cells in the bladder wall. Studies on smooth muscle function often do not take the origin of smooth muscle cells into account i.e., whether they were harvested from normal or overactive bladders. Although, this simplistic view may be beneficial to understanding the generation of the spontaneous activity of the bladder, however, it does not sufficiently explain the cell-to-cell propagation of the spontaneous smooth muscle activity. The spontaneous activity of smooth muscle is an important factor that works against the bladder compliance in the filling phase, and may inversely affect the neurally evoked response during micturition. The intensity of spontaneous activity is the age-dependent; it is high in neonatal bladders it is small or almost non-existent in adults and reemerges in older bladders. This review focuses on these age-dependent alterations of spontaneous bladder contractions and describes the possible mechanisms which may have important role in regulating the spontaneous contractions using the rat as an animal model.
Collapse
Affiliation(s)
- Gyula P Szigeti
- Department of Physiology, Medical-, Health- and Science Centre, University of Debrecen, Hungary.
| | | | | | | |
Collapse
|
23
|
Ramanan SV, Valiunas V, Brink PR. Non-stationary fluctuation analysis of macroscopic gap junction channel records. J Membr Biol 2005; 205:81-8. [PMID: 16283588 PMCID: PMC1440518 DOI: 10.1007/s00232-005-0765-4] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2005] [Revised: 08/04/2005] [Indexed: 10/25/2022]
Abstract
Non-stationary fluctuation analysis was applied to macroscopic records of junctional currents arising from homotypic Cx37 and Cx43 gap junction channels expressed in RIN cells. The data were analyzed by a modification of existing analytical methods that takes endemic uncoupling into account. The results are consistent with both channels having open probabilities ranging from 0.7 to near unity for low transjunctional voltages. The analysis also yielded estimates of single-channel conductances for the two channel types similar to those seen in single-channel recordings. The results presented here show that fluctuation analysis can be used to extract single-channel gap junctional conductances from macroscopic double whole-cell recordings. These results also constitute empirically determined estimates of the open probability that are not model-dependent.
Collapse
Affiliation(s)
- S V Ramanan
- AU-KBC Research Center, MIT, Chromepet, Chennai 600044, India.
| | | | | |
Collapse
|
24
|
Mukherjee S, Huang H, Petkova SB, Albanese C, Pestell RG, Braunstein VL, Christ GJ, Wittner M, Lisanti MP, Berman JW, Weiss LM, Tanowitz HB. Trypanosoma cruzi infection activates extracellular signal-regulated kinase in cultured endothelial and smooth muscle cells. Infect Immun 2004; 72:5274-82. [PMID: 15322023 PMCID: PMC517449 DOI: 10.1128/iai.72.9.5274-5282.2004] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 05/03/2004] [Accepted: 06/11/2004] [Indexed: 11/20/2022] Open
Abstract
Trypanosoma cruzi infection causes cardiomyopathy and vasculopathy. We examined the consequence of this infection for the mitogen-activated protein kinase (MAPK) pathways, which regulate cell proliferation in cultured human umbilical vein endothelial and vascular smooth muscle cells. Infection of these cells resulted in activation of extracellular signal-regulated kinases 1and 2 (ERK1/2) but not c-Jun N-terminal kinase or p38 MAPK. Treatment of these cells with the MAPK kinase inhibitor PD98059 prior to infection blocked the increase in phosphorylated ERK1/2 seen with infection. Heat-killed parasites did not activate ERK1/2, indicating that activation of ERK1/2 was dependent on infection of these cells by live parasites. Furthermore, transfection with dominant-negative Raf(301) or Ras(N17) constructs reduced the infection-associated levels of phospho-ERK1/2, indicating that the activation of ERK1/2 involved the Ras-Raf-ERK pathway. Infection also resulted in an increase in activator protein 1 (AP-1) activity, which was inhibited by transfection with a dominant-negative Raf(301) construct. T. cruzi-infected endothelial cells secreted endothelin-1 and interleukin-1beta, which activated ERK1/2 and induced cyclin D1 expression in uninfected smooth muscle cells. These data suggest a possible molecular paradigm for the pathogenesis of the vasculopathy and the cardiovascular remodeling associated with T. cruzi infection.
Collapse
Affiliation(s)
- Shankar Mukherjee
- Department of Pathology, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, NY 10461, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
25
|
Seki A, Duffy HS, Coombs W, Spray DC, Taffet SM, Delmar M. Modifications in the biophysical properties of connexin43 channels by a peptide of the cytoplasmic loop region. Circ Res 2004; 95:e22-8. [PMID: 15284189 DOI: 10.1161/01.res.0000140737.62245.c5] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Connexin43 (Cx43) channels reside in at least 3 states: closed, open, or residual. It is hypothesized that the residual state results from the interaction of an intracellular "gating element" with structures at the vestibule of the pore. Recently, we showed in vitro that there is an intramolecular interaction of the carboxyl-terminal domain (referred to as "CT") with a region in the cytoplasmic loop of Cx43 (amino acids 119 to 144; referred to as "L2"). Here, we assessed whether the L2 region was able to interact with the gating particle in a functional channel. Cx43 channels were recorded in the presence of a peptide corresponding to the L2 region, delivered via the patch pipette. This manipulation did not modify unitary conductance, but decreased the frequency of transitions into the residual state, prolonged open time, and altered the voltage dependence of the channel in a manner analogous to that observed after truncation of the CT domain. The latter correlated with the ability of the peptide to bind to the CT domain, as determined by mirror resonance spectroscopy. Overall, we propose that the L2 acts as a "receptor" that interacts with a flexible intracellular gating element during channel gating. The full text of this article is available online at http://circres.ahajournals.org.
Collapse
Affiliation(s)
- Akiko Seki
- Department of Pharmacology, State University of New York Upstate Medical University, Syracuse 13210, USA
| | | | | | | | | | | |
Collapse
|
26
|
Gemel J, Valiunas V, Brink PR, Beyer EC. Connexin43 and connexin26 form gap junctions, but not heteromeric channels in co-expressing cells. J Cell Sci 2004; 117:2469-80. [PMID: 15128867 DOI: 10.1242/jcs.01084] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Many cells contain two (or more) gap junction proteins that are able to oligomerize with each other to form heteromeric gap junction channels and influence the properties of intercellular communication. Cx26 and Cx43 are found together in a number of cell types, but previous data have suggested that they might not form heteromeric connexons. We studied the possible interactions of these connexins by co-expression in three different cell lines. Analysis of N2aCx26/Cx43 cell pairs by double whole-cell patch-clamp methods showed that these cells were coupled, but contained only a small number of sizes of single channels consistent with those formed by homomeric Cx26 or Cx43 channels. Immunofluorescence studies showed that both connexins localized to appositional membranes, but in largely distinct domains. Analysis of Triton X-100-solubilized connexons from co-expressing cells by centrifugation through sucrose gradients or by affinity purification using a Ni-NTA column showed no evidence of mixing of Cx26 and Cx43. These results contrast with our observations in cells co-expressing other connexins with Cx43 and suggest that Cx26 and Cx43 do not form heteromeric hemichannels. Moreover, the incorporation of Cx26 and Cx43 into oligomers and into the membrane were similarly affected by treatment of co-expressing cells with brefeldin A or nocodazole, suggesting that the lack of mixing is due to incompatibility of these connexins, not to differences in biosynthetic trafficking.
Collapse
Affiliation(s)
- Joanna Gemel
- Department of Pediatrics, Section of Hematology/Oncology and Stem Cell Transplantation, University of Chicago, IL 60637-1470, USA
| | | | | | | |
Collapse
|
27
|
Alexander DB, Ichikawa H, Bechberger JF, Valiunas V, Ohki M, Naus CCG, Kunimoto T, Tsuda H, Miller WT, Goldberg GS. Normal cells control the growth of neighboring transformed cells independent of gap junctional communication and SRC activity. Cancer Res 2004; 64:1347-58. [PMID: 14973064 DOI: 10.1158/0008-5472.can-03-2558] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The growth of many types of cancer cells can be controlled by surrounding normal cells. However, mechanisms underlying this phenomenon have not been defined. We used a layered culture system to investigate how nontransformed cells suppress the growth of neighboring transformed cells. Direct physical contact between transformed and nontransformed cells was required for growth suppression of transformed cells in this system; communication by diffusible factors was not sufficient. However, significant gap junctional communication was not required, indicating that other intercellular junctions mediated this growth regulatory response. We also report that the Src kinase activity in transformed cells was not directly inhibited by contact with nontransformed cells. Instead, nontransformed cells increased the expression of serum deprivation-response protein and the transcription factor four and a half LIM domain 1 in tumor cells. In addition, these results suggest mechanisms by which normal cells may block Wnt signaling, inhibit insulin-like growth factor activity, and promote host recognition of neighboring tumor cells.
Collapse
Affiliation(s)
- David B Alexander
- Department of Physiology and Biophysics, School of Medicine, Health Sciences Complex, State University of New York at Stony Brook, Stony Brook, NY 11794-8661, USA
| | | | | | | | | | | | | | | | | | | |
Collapse
|
28
|
Christ GJ, Day NS, Day M, Zhao W, Persson K, Pandita RK, Andersson KE. Increased connexin43-mediated intercellular communication in a rat model of bladder overactivity in vivo. Am J Physiol Regul Integr Comp Physiol 2003; 284:R1241-8. [PMID: 12676745 DOI: 10.1152/ajpregu.00030.2002] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bladder overactivity associated with outflow obstruction is a common human condition recapitulated in the female rat by narrowing the diameter of the urethra. The goal of these studies was to evaluate the role of intercellular communication through connexin43 (Cx43)-derived gap junction channels to bladder overactivity following partial urethral outflow obstruction of 3-day to 6-wk duration. Cx43 mRNA and protein expression were barely detectable by Northern or Western blots, respectively, in the detrusor layer of normal bladders, but bands were found with both techniques after 6 wk of obstruction. Linear regression analysis of the RT-PCR data revealed a statistically significant positive correlation between the duration of obstruction (again, ranging from 3-day to 6-wk duration) and Cx43 mRNA transcript levels, such that after 6 wk of obstruction, Cx43 transcript levels were approximately 15-fold greater than initial control values. When taking into account the approximately fivefold increase in bladder weight over this same time frame, the absolute amount of Cx43 mRNA in the bladder apparently increased by approximately 75-fold. In that regard, as anticipated, and consistent with previous observations, 6 wk of obstruction was also associated with a significant increase in spontaneous bladder contractions between micturitions. The amplitude of these contractions was significantly reduced by heptanol given intravesically. Furthermore, carbachol-precontracted bladder strips from obstructed animals were more sensitive to heptanol-induced relaxation (100 microM) than their unobstructed counterparts (n = 6; P < 0.01). When bladder strips were equivalently precontracted via electrical field stimulation (EFS; 20 Hz), similar heptanol-induced relaxation responses were observed. However, the tetrodotoxin-resistant portion of the EFS-induced contraction was greater in the obstructed than in the unobstructed animals, and this portion of the contractile response was more sensitive to heptanol-induced relaxation in obstructed than unobstructed bladders (n = 7; P < 0.01). Taken together, these observations indicate that partial outlet obstruction produces an overactive bladder that may be more dependent on intercellular communication through gap junctions for modulation of contractile responses than its normal counterpart.
Collapse
Affiliation(s)
- George J Christ
- Departments of Urology and Physiology and Biophysics, Institute for Smooth Muscle Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
| | | | | | | | | | | | | |
Collapse
|
29
|
Christ GJ, Venkateswarlu K, Day NS, Valcic M, Santizo C, Zhao W, Wang HZ, Persson K, Andersson KE. Intercellular communication and bladder function. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2003; 539:239-54. [PMID: 15088908 DOI: 10.1007/978-1-4419-8889-8_17] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
There is now considerable experimental and clinical evidence supporting the supposition that overactivity of the bladder is associated with detectable alterations in the electrical properties of the detrusor smooth muscle cells. The preliminary data described in this report indicates that intercellular communication through gap junctions might play an important role in this process. Moreover, alterations in Cx43 mRNA expression may represent a tissue response to a physiologic insult (i.e., increased after load) in an attempt to further increase the syncytial nature and force of detrusor contractility to compensate for an increased pressure load. Finally, this report elucidates the rationale for suspecting that intercellular communication through gap junctions may play a role in normal bladder physiology and the pathophysiology of urinary incontinence caused by partial outlet obstruction.
Collapse
Affiliation(s)
- George J Christ
- Department of Urology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
30
|
Abstract
Gap junction channels are low resistance pathways allowing an action potential to propagate from one cell to the neighboring. Moreover, small molecules (<1000 Da) may pass the channel providing a possibility for metabolic coupling, growth and differentiation control of a cell by its surrounding. Antiarrhythmic peptides can enhance the conductivity of the channels while other peptides, angiotensin or extracellular loop peptides, reduce intercellular communication. On the other hand, peptides like angiotensin II or endothelin-1 can increase expression of certain gap junction channel proteins and, thereby, may affect intercellular coupling chronically. Thus, intercellular communication can be controlled using peptide drugs.
Collapse
Affiliation(s)
- Stefan Dhein
- Clinic for Cardiac Surgery, Heart Center, University of Leipzig, Leipzig, Germany.
| |
Collapse
|
31
|
Abstract
Several proteins including connexin40 (Cx40) and connexin43 (Cx43) form gap junctions between cells of the heart; they may be found separately or may be coexpressed. These connexins form channels with differing conductance and permeability properties. Cx40 and Cx43 are each required for normal electrical conduction between cells in different regions of the heart. We hypothesized that the major difference between these connexins might be in their selective intercellular passage of small molecules such as second messengers, which can be assessed using biologically inert fluorescent probes. Therefore, we designed experimental paradigms to quantitate the permeability properties of these cardiac connexins using simultaneous measurement of junctional conductance (g(j)) by the double whole-cell patch-clamp technique and intercellular transfer of Lucifer Yellow (LY) by fluorescence microscopy. These studies were performed in HeLa cells stably transfected with Cx40 or Cx43 or cotransfected with both connexins. We found that homotypic Cx43 channels were about 5 times more permeable to LY than homotypic Cx40 channels (flux of approximately 1560 versus approximately 300 molecules/channel per second). Channels between heterotypic (Cx40-Cx43) cell pairs and between pairs of coexpressing cells exhibited intermediate LY permeability. The permeability ratio for LY relative to monovalent cation (K+) ranged from 0.0025 for Cx40 to 0.028 for Cx43. These permeability ratios suggest that the connexins are highly selective for solutes in the size and charge range of many second messengers. Moreover, the data indicate that coexpression of connexins does not generate unique permeability characteristics, but rather results in an intermediate permeability for solutes involved in metabolic/biochemical coupling.
Collapse
Affiliation(s)
- Virginijus Valiunas
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794, USA
| | | | | |
Collapse
|
32
|
Popp R, Brandes RP, Ott G, Busse R, Fleming I. Dynamic modulation of interendothelial gap junctional communication by 11,12-epoxyeicosatrienoic acid. Circ Res 2002; 90:800-6. [PMID: 11964373 DOI: 10.1161/01.res.0000015328.20581.d6] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Functional gap junctional communication between vascular cells has been implicated in ascending dilatation and the cytochrome P-450 (CYP) inhibitor-sensitive and NO- and prostacyclin-independent dilatation of many vascular beds. Here, we assessed the mechanisms by which the epoxyeicosatrienoic acids (EETs) generated by a CYP 2C enzyme control interendothelial gap junctional communication. In CYP 2C-expressing porcine coronary endothelial cells, bradykinin, which enhances EET formation, elicited a biphasic effect on the electrical coupling and transfer of Lucifer yellow between endothelial cells, consisting of a transient increase in coupling followed by a sustained uncoupling. The initial phase was sensitive to the CYP 2C9 inhibitor sulfaphenazole and the protein kinase A (PKA) inhibitors Rp-cAMPS and KT5720 and could be mimicked by forskolin and caged cAMP as well as by the PKA activators 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole 3',5'-cyclic monophosphorothioate sodium salt and Sp-cAMPS. Gap junction uncoupling in bradykinin-stimulated porcine coronary endothelial cells was prevented by inhibiting the activation of extracellular signal-regulated kinase (ERK)1/2. In human endothelial cells, which express little CYP 2C, bradykinin elicited only an ERK1/2-mediated inhibition of intercellular communication. The CYP 2C9 product, 11,12-EET, also exerted a dual effect on the electrical and dye coupling of human endothelial cells, which was sensitive to PKA inhibition. These results demonstrate that an agonist-activated CYP-dependent pathway as well as 11,12-EET can positively regulate interendothelial gap junctional communication, most probably via the activation of PKA, an effect that is curtailed by the subsequent activation of ERK1/2.
Collapse
Affiliation(s)
- Rüdiger Popp
- Institut für Kardiovaskuläre Physiologie, Klinikum der J.W.G.-Universität, Frankfurt am Main, Germany
| | | | | | | | | |
Collapse
|
33
|
Valiunas V. Biophysical properties of connexin-45 gap junction hemichannels studied in vertebrate cells. J Gen Physiol 2002; 119:147-64. [PMID: 11815665 PMCID: PMC2233802 DOI: 10.1085/jgp.119.2.147] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2001] [Revised: 12/27/2001] [Accepted: 12/27/2001] [Indexed: 11/20/2022] Open
Abstract
Human HeLa cells transfected with mouse Cx45 and rat RIN cells transfected with chicken Cx45 were used to study the electrical and permeability properties of Cx45 gap junction hemichannels. With no extracellular Ca(2+), whole-cell recording revealed currents arising from hemichannels in both transfected cell lines. Multichannel currents showed a time-dependent activation or deactivation sensitive to voltage, V(m). These currents did not occur in non-transfected cells. The hemichannel currents were inhibited by raising extracellular Ca(2+) or by acidification with CO(2). The unitary conductance exhibited V(m) dependence (i.e., gamma(hc,main) increased/decreased with hyperpolarization/depolarization). Extrapolation to V(m) = 0 mV led to a gamma(hc,main) of 57 pS, roughly twice the conductance of an intact Cx45 gap junction channel. The open channel probability, P(o), was V(m)-dependent, declining at negative V(m) (P(o) < 0.11, V(m) < -50 mV), and increasing at positive V(m) (P(o) approximately 0.76, V(m) > 50 mV). Moreover, Cx45 nonjunctional hemichannels appeared to mediate lucifer yellow (LY) and propidium iodide (PI) dye uptake from the external solution when extracellular Ca(2+) level was reduced. Dye uptake was directly proportional to the number of functioning hemichannels. No significant dye uptake was detected in non-transfected cells. Cx45 transfected HeLa and RIN cells also allowed dye to leak out when preloaded with LY and then incubated in Ca(2+)-free external solution, whereas little or no dye leakage was observed when these cells were incubated with 2 mM external Ca(2+). Intact Cx45 gap junction channels allowed passage of either LY or PI dye, but their respective flux rates were different. Comparison of LY diffusion through Cx45 hemichannels and intact gap junction channels revealed that the former is more permeable, suggesting that gap junction channel pores exhibit more allosterical restriction to the dye molecules than the unopposed hemichannel. The data demonstrate the opening of Cx45 nonjunctional hemichannels in vertebrate cells when the external Ca(2+) concentration is reduced.
Collapse
Affiliation(s)
- Virginijus Valiunas
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, NY 11794, USA.
| |
Collapse
|
34
|
Chen-Izu Y, Moreno AP, Spangler RA. Opposing gates model for voltage gating of gap junction channels. Am J Physiol Cell Physiol 2001; 281:C1604-13. [PMID: 11600424 DOI: 10.1152/ajpcell.2001.281.5.c1604] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gap junctions are intercellular channels that link the cytoplasm of neighboring cells. Because a gap junction channel is composed of two connexons docking head-to-head with each other, the channel voltage-gating profile is symmetrical for homotypic channels made of two identical connexons (hemichannels) and asymmetric for the heterotypic channels made of two different connexons (i.e., different connexin composition). In this study we have developed a gating model that allows quantitative characterization of the voltage gating of homotypic and heterotypic channels. This model differs from the present model in use by integrating, rather than separating, the contributions of the voltage gates of the two member connexons. The gating profile can now be fitted over the entire voltage range, eliminating the previous need for data splicing and fusion of two hemichannel descriptions, which is problematic when dealing with heterotypic channels. This model also provides a practical formula to render quantitative several previously qualitative concepts, including a similarity principle for matching a voltage gate to its host connexon, assignment of gating polarity to a connexon, and the effect of docking interactions between two member connexons in an intact gap junction channel.
Collapse
Affiliation(s)
- Y Chen-Izu
- Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
| | | | | |
Collapse
|
35
|
Valiunas V, Gemel J, Brink PR, Beyer EC. Gap junction channels formed by coexpressed connexin40 and connexin43. Am J Physiol Heart Circ Physiol 2001; 281:H1675-89. [PMID: 11557558 DOI: 10.1152/ajpheart.2001.281.4.h1675] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Many cardiovascular cells coexpress multiple connexins (Cx), leading to the potential formation of mixed (heteromeric) gap junction hemichannels whose biophysical properties may differ from homomeric channels containing only one connexin type. We examined the potential interaction of connexin Cx43 and Cx40 in HeLa cells sequentially stably transfected with these two connexins. Immunoblots verified the production of comparable amounts of both connexins, cross-linking showed that both connexins formed oligomers, and immunofluorescence showed extensive colocalization. Moreover, Cx40 copurified with (His)(6)-tagged Cx43 by affinity chromatography of detergent-solubilized connexons, demonstrating the presence of both connexins in some hemichannels. The dual whole cell patch-clamp method was used to compare the gating properties of gap junctions in HeLa Cx43/Cx40 cells with homotypic (Cx40-Cx40 and Cx43-Cx43) and heterotypic (Cx40-Cx43) gap junctions. Many of the observed single channel conductances resembled those of homotypic or heterotypic channels. The steady-state junctional conductance (g(j,ss)) in coexpressing cell pairs showed a reduced sensitivity to the voltage between cells (V(j)) compared with homotypic gap junctions and/or an asymmetrical V(j) dependence reminiscent of heterotypic gap junctions. These gating properties could be fit using a combination of homotypic and heterotypic channel properties. Thus, whereas our biochemical evidence suggests that Cx40 and Cx43 form heteromeric connexons, we conclude that they are functionally insignificant with regard to voltage-dependent gating.
Collapse
Affiliation(s)
- V Valiunas
- Department of Physiology and Biophysics, State University of New York, Stony Brook, New York 11794, USA
| | | | | | | |
Collapse
|
36
|
Wang HZ, Day N, Valcic M, Hsieh K, Serels S, Brink PR, Christ GJ. Intercellular communication in cultured human vascular smooth muscle cells. Am J Physiol Cell Physiol 2001; 281:C75-88. [PMID: 11401829 DOI: 10.1152/ajpcell.2001.281.1.c75] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Intercellular communication through gap junction channels plays a fundamental role in regulating vascular myocyte tone. We investigated gap junction channel expression and activity in myocytes from the physiologically distinct vasculature of the human internal mammary artery (IMA, conduit vessel) and saphenous vein (SV, capacitance vessel). Northern and Western blots documented the presence of connexin43 (Cx43) in frozen tissues and cultured cells from both vessels. Northern blots also confirmed the presence of Cx40 mRNA in cultured IMA and SV myocytes. Dual whole cell patch-clamp experiments revealed that macroscopic junctional conductance was voltage dependent and characteristic of that observed for Cx43. In the majority of records, in both vessels, single-channel activity was dominated by a main-state conductance of 120 pS, with subconducting events comprising less than 10% of the amplitude histograms. However, some records showed "atypical" unitary events that had a conductance similar to Cx40 (approximately 140-160 pS), but gating behavior like that of Cx43. As such, it is conceivable that the presence and coexpression of Cx40 and Cx43 in IMA and SV myocytes may result in heteromeric channel formation. Nonetheless, in terms of gating, Cx43-like behavior clearly dominates.
Collapse
Affiliation(s)
- H Z Wang
- Department of Urology, Institute for Smooth Muscle Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA
| | | | | | | | | | | | | |
Collapse
|
37
|
Abstract
Electrical activation of the heart requires cell-cell transfer of current via gap junctions, arrays of densely packed protein channels that permit intercellular passage of ions and small molecules. Because current transfer occurs only at gap junctions, the spatial distribution and biophysical properties of gap junction channels are important determinants of the conduction properties of cardiac muscle. Gap junction channels are composed of members of a multigene family of proteins called connexins. As a general rule, individual cells express multiple connexins, which creates the potential for considerable functional diversity in gap junction channels. Although gap junction channels are relatively nonselective in their permeability to ions and small molecules, cardiac myocytes actively adjust their level of coupling by multiple mechanisms including changes in connexin expression, regulation of connexin trafficking and turnover, and modulation of channel properties. In advanced stages of heart disease, connexin expression and intercellular coupling are diminished, and gap junction channels become redistributed. These changes have been strongly implicated in the pathogenesis of lethal ventricular arrhythmias. Ongoing studies in genetically engineered mice are revealing insights into the role of individual gap junction channel proteins in normal cardiac function and arrhythmogenesis.
Collapse
Affiliation(s)
- S Kanno
- Department of Surgery and the Center for Cardiovascular Research, Washington University School of Medicine, St. Louis, MO 63110, USA
| | | |
Collapse
|
38
|
Melman A, Christ GJ. Integrative erectile biology. The effects of age and disease on gap junctions and ion channels and their potential value to the treatment of erectile dysfunction. Urol Clin North Am 2001; 28:217-31, vii. [PMID: 11402576 DOI: 10.1016/s0094-0143(05)70133-6] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
Initiation, maintenance, and modulation of corporal smooth muscle tone are critically dependent upon agonist-induced changes in intracellular calcium levels and mobilization as well as transmembrane calcium flux. The transient control of myocyte excitability and contractility at the cellular level is inextricably linked to membrane potential, which, in turn, is modulated by potassium ion efflux through one of the four known corporeal smooth muscle potassium ion channels. Corporal tissue responses are subsequently coordinated by means of the movement of intracellular second messenger molecules (i.e., IP3, cAMP, cGMP) and ions (i.e., K+ and Ca2+) among the corporal myocytes by means of intercellular communication through gap junction channels. Knowledge of the critical contribution of these interlinking cellular (nonjunctional ion channels [e.g., maxi-K]) and tissue (gap junction channels [e.g., connexin 43]) systems to the modulation of erectile capacity has provided the scientific rationale for the promulgation of the successful preclinical testing of hSlo ion channel gene therapy for the normalization of erectile status in both aged and diabetic rats.
Collapse
Affiliation(s)
- A Melman
- Department of Urology, Institute for Smooth Muscle Biology, Montefiore Medical Center/Albert Einstein College of Medicine, Bronx, New York, USA
| | | |
Collapse
|
39
|
Abstract
Electrical activation of the heart requires current transfer from one cell to another via gap junctions, arrays of densely packed intercellular channels. The extent to which cardiac myocytes are coupled is determined by multiple mechanisms, including tissue-specific patterns of expression of diverse gap junction channel proteins (connexins), and regulatory pathways that control connexin synthesis, intracellular trafficking, assembly into channels, and degradation. Many connexins, including those expressed in the heart, have been found to turn over rapidly. Recent studies in the intact adult heart suggest that connexin43, the principal cardiac connexin, is surprisingly short-lived (half-life approximately 1.3 hours). Both the proteasome and the lysosome participate in connexin43 degradation. Other ion channel proteins, such as those forming selected voltage-gated K(+) channels, may also exhibit rapid turnover kinetics. Regulation of connexin degradation may be an important mechanism for adjusting intercellular coupling in the heart under normal and pathophysiological conditions.
Collapse
Affiliation(s)
- J E Saffitz
- Departments of Pathology and Medicine and the Center for Cardiovascular Research, Washington University, St. Louis, MO 63110, USA.
| | | | | |
Collapse
|
40
|
Christ GJ, Brink PR. Gap junctions in isolated rat aorta: evidence for contractile responses that exhibit a differential dependence on intercellular communication. Braz J Med Biol Res 2000; 33:423-9. [PMID: 10775307 DOI: 10.1590/s0100-879x2000000400008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Connexin43 (Cx43) is a major gap junction protein present in the Fischer-344 rat aorta. Previous studies have identified conditions under which selective disruption of intercellular communication with heptanol caused a significant, readily reversible and time-dependent diminution in the magnitude of alpha1-adrenergic contractions in isolated rat aorta. These observations have indentified a significant role for gap junctions in modulating vascular smooth muscle tone. The goal of these steady-state studies was to utilize isolated rat aortic rings to further evaluate the contribution of intercellular junctions to contractions elicited by cellular activation in response to several other vascular spasmogens. The effects of heptanol were examined (0.2-2.0 mM) on equivalent submaximal ( approximately 75% of the phenylephrine maximum) aortic contractions elicited by 5-hydroxytryptamine (5-HT; 1-2 microM), prostaglandin F2alpha (PGF2alpha; 1 microM) and endothelin-1 (ET-1; 20 nM). Statistical analysis revealed that 200 microM and 500 microM heptanol diminished the maximal amplitude of the steady-state contractile responses for 5-HT from a control response of 75 +/- 6% (N = 26 rings) to 57 +/- 7% (N = 26 rings) and 34.9 +/- 6% (N = 13 rings), respectively (P<0.05), and for PGF2alpha from a control response of 75 +/- 10% (N = 16 rings) to 52 +/- 8% (N = 19 rings) and 25.9 +/- 6% (N = 18 rings), respectively (P<0.05). In contrast, 200 microM and 500 microM heptanol had no detectable effect on the magnitude of ET-1-induced contractile responses, which were 76 +/- 5. 0% for the control response (N = 38 rings), 59 +/- 6.0% in the presence of 200 microM heptanol (N = 17 rings), and 70 +/- 6.0% in the presence of 500 microM heptanol (N = 23 rings) (P<0.13). Increasing the heptanol concentration to 1 mM was associated with a significant decrease in the magnitude of the steady-state ET-1-induced contractile response to 32 +/- 5% (21 rings; P<0.01); further increasing the heptanol concentration to 2 mM had no additional effect. In rat aorta then, junctional modulation of tissue contractility appears to be agonist-dependent.
Collapse
Affiliation(s)
- G J Christ
- Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | | |
Collapse
|
41
|
Brink PR, Ricotta J, Christ GJ. Biophysical characteristics of gap junctions in vascular wall cells: implications for vascular biology and disease. Braz J Med Biol Res 2000; 33:415-22. [PMID: 10775306 DOI: 10.1590/s0100-879x2000000400007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The role gap junction channels play in the normal and abnormal functioning of the vascular wall is the subject of much research. The biophysical properties of gap junctions are an essential component in understanding how gap junctions function to allow coordinated relaxation and contraction of vascular smooth muscle. This study reviews the properties thus far elucidated and relates those properties to tissue function. We ask how biophysical and structural properties such as gating, permselectivity, subconductive states and channel type (heteromeric vs homotypic vs heterotypic) might affect vascular smooth muscle tone.
Collapse
Affiliation(s)
- P R Brink
- Physiology and Biophysics, Institute for Molecular Cardiology, SUNY at Stony Brook, NY 11794, USA
| | | | | |
Collapse
|
42
|
Abstract
Gap junctions formed between transfected cells expressing connexin (Cx) 40 and Cx43 (Cx43-RIN, Cx40-HeLa, and Cx43-HeLa) revealed a relationship, g(j)=f(V(j)), at steady state, that is typified by a nonsymmetrical behavior similar to that previously reported for other heterotypic channels (gap junction conductance [g(j)]; transjunctional voltage [V(j)]). The unitary conductance of the channels was sensitive to the polarity of V(j). A main state conductance of 61 pS was found when the Cx43 cell was stepped positively or the Cx40 cell negatively (V(j)=70 mV); the reverse polarities yielded a conductance of 100 pS. These heterotypic channels were permeable to carboxyfluorescein. In addition, two other heterotypic forms are illustrated to demonstrate that endogenous Cx45 expression cannot explain the results. The demonstration of heterotypic Cx40-Cx43 channels may have implications for the propagation of the electrical impulse in heart. For example, they may contribute to the slowing of the impulse propagation through the junctions between Purkinje fibers and ventricular muscle.
Collapse
Affiliation(s)
- V Valiunas
- Department of Physiology and Biophysics, State University of New York at Stony Brook, NY 11794, USA
| | | | | |
Collapse
|
43
|
Valiunas V, Manthey D, Vogel R, Willecke K, Weingart R. Biophysical properties of mouse connexin30 gap junction channels studied in transfected human HeLa cells. J Physiol 1999; 519 Pt 3:631-44. [PMID: 10457079 PMCID: PMC2269545 DOI: 10.1111/j.1469-7793.1999.0631n.x] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/1999] [Accepted: 06/22/1999] [Indexed: 11/27/2022] Open
Abstract
1. Human HeLa cells expressing mouse connexin30 (Cx30) were used to study the electrical properties of Cx30 gap junction channels. Experiments were performed on cell pairs with the dual voltage-clamp method. 2. The gap junction conductance (gj) at steady state showed a bell-shaped dependence on junctional voltage (Vj; Boltzmann fit: Vj,0 = 27 mV, gj,min = 0.15, z = 4). The instantaneous gj decreased slightly with increasing Vj. 3. The gap junction currents (Ij) declined with time following a single exponential. The time constants of Ij inactivation (taui) decreased with increasing Vj. 4. Single channels exhibited a main state, a residual state and a closed state. The conductances gammaj,main and gammaj,residual were 179 and 48 pS, respectively (pipette solution, potassium aspartate; temperature, 36-37 degrees C; extrapolated to Vj = 0 mV). 5. The conductances gammaj,residual and gammaj,main showed a slight Vj dependence and were sensitive to temperature (Q10 values of 1.28 and 1.16, respectively). 6. Current transitions between open states (i.e. main state, substates, residual state) were fast (< 2 ms), while those between an open state and the closed state were slow (12 ms). 7. The open channel probability (Po) at steady state decreased from 1 to 0 with increasing Vj (Boltzmann fit: Vj,0 = 37 mV; z = 3). 8. Histograms of channel open times implied the presence of a single main state; histograms of channel closed times suggested the existence of two closed states (i.e. residual states). 9. We conclude that Cx30 channels are controlled by two types of gates, a fast one responsible for Vj gating involving transitions between open states (i.e. residual state, main state), and a slow one correlated with chemical gating involving transitions between the closed state and an open state.
Collapse
Affiliation(s)
- V Valiunas
- Department of Physiology, University of Bern, Buhlplatz 5, CH-3012 Bern, Switzerland
| | | | | | | | | |
Collapse
|
44
|
Abstract
Three connexins, Cx43, Cx40, and Cx37, have been found by protein or mRNA analysis to be prominent in mammalian blood vessels, but electrophysiological characterization of gap junction channels in freshly isolated vascular smooth muscle cells (SMCs) has not previously been reported. We used a dual-perforated patch-clamp technique to study gap junction conductances in SMC pairs from rat basilar arteries. Macroscopic junctional conductance (Gj) measured in 98 cell pairs with either Cs+ or K+ ranged between 0.68 and 24.8 nS. In weakly coupled cells (Gj<5 nS), single-channel currents were readily resolved without pharmacological uncoupling agents, allowing identification of 4 major unitary conductances. Two of these conductances, 80 to 120 pS and 150 to 200 pS, corresponded to the major conductance states for homotypic channels formed from Cx43 or Cx40, which we confirmed were present in smooth muscle by immunofluorescence analysis. Two other conductances, 220 to 280 pS and >300 pS, were identified that have not been previously reported in vascular SMCs. Macroscopic recordings revealed currents that deactivated incompletely over a broad range of transjunctional potentials. In about half of the pairs, we identified macroscopic as well as single-channel currents that exhibited marked voltage asymmetry, consistent with nonhomotypic, ie, either heterotypic or heteromeric channels. Our data indicate that basilar artery SMCs are coupled in vivo in a richly complex manner, involving Cx43, Cx40, and other large-conductance channels, and that a significant number of couplings involve putative nonhomotypic channels.
Collapse
Affiliation(s)
- X Li
- Departments of Neurosurgery and Physiology, University of Maryland School of Medicine, Baltimore, MD, USA
| | | |
Collapse
|
45
|
Christ GJ, Spektor M, Brink PR, Barr L. Further evidence for the selective disruption of intercellular communication by heptanol. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 276:H1911-7. [PMID: 10362670 DOI: 10.1152/ajpheart.1999.276.6.h1911] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The lack of selective gap junctional uncoupling agents has hampered evaluation of the contribution of intercellular communication to pharmacomechanical coupling and vascular contractility. Thus we further explored the utility and selectivity of heptanol as a gap junctional uncoupling agent in isolated rat aortic rings. Fifty-two aortic rings were obtained from 15 rats and were precontracted to approximately 75% of maximum with phenylephrine (PE). When contraction achieved steady state (approximately 5 min), a single concentration of heptanol (200 microM) was added to each aortic ring at 1- to 3-min intervals for up to 42 min post-PE addition. At early time points (5-10 min after PE), heptanol elicited an approximately 50% loss of tension (i.e., relaxation). At subsequent time points post-PE, a gradual and time-dependent decrease in the magnitude of the heptanol-induced relaxation was observed until, after approximately 40 min, addition of heptanol was associated with little, if any, detectable relaxation. Linear regression analysis of the magnitude of the heptanol-induced relaxation vs. the square root of the elapsed time interval (from addition of PE) revealed a highly significant negative correlation (P < 0.001, R = 0.81). Studies conducted on KCl-precontracted aortic rings revealed no detectable heptanol-induced relaxation after development of the steady-state KCl-induced contraction. These data extend our previous observations to further document the potential utility of heptanol as a "relatively selective" uncoupling agent.
Collapse
Affiliation(s)
- G J Christ
- Laboratory of Molecular and Integrative Urology, Department of Urology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
| | | | | | | |
Collapse
|
46
|
Ramanan SV, Brink PR, Varadaraj K, Peterson E, Schirrmacher K, Banach K. A three-state model for connexin37 gating kinetics. Biophys J 1999; 76:2520-9. [PMID: 10233068 PMCID: PMC1300223 DOI: 10.1016/s0006-3495(99)77406-0] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
Abstract
The gating behavior of human connexin 37 (hCx37) is unaffected by the nature of the bathing monovalent (for Na, K, Rb). It is modified by [Mg] in the millimolar range. For fitting the kinetics, we propose a simple extension to three states of the canonical 2-state model of the hemichannel. The extra closed state allows for some immobilization of a hemichannel at high transjunctional voltages. The model is reasonably efficient at fitting data at various voltage protocols. Interpreting the fits of the data at different [Mg] is consistent with a binding site for Mg.
Collapse
Affiliation(s)
- S V Ramanan
- Department of Physiology and Biophysics, State University of New York at Stony Brook, Stony Brook, New York 11794-8661, USA
| | | | | | | | | | | |
Collapse
|
47
|
Christ GJ, Brink PR. Analysis of the presence and physiological relevance of subconducting states of Connexin43-derived gap junction channels in cultured human corporal vascular smooth muscle cells. Circ Res 1999; 84:797-803. [PMID: 10205147 DOI: 10.1161/01.res.84.7.797] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Subconductance states are a commonly observed feature of gap junction channels. Their overt frequency and consistent appearance in both single and multichannel records have led to speculation that they might be of physiological importance in terms of altering the rate of small solute transfer from cell to cell. Among the connexin gene family, connexin43 (Cx43) is the most ubiquitous connexin that has been shown to generate subconductive states. Therefore, it was the explicit aim of this investigation to more fully evaluate the potential contribution of human Cx43-derived subconducting states to intercellular communication in cultured human corporal vascular smooth muscle cells. To determine the weight of subconductive states in our records, we analyzed amplitude histograms of multichannel and single-channel data during the application of transjunctional voltages larger than expected for physiological conditions but still smaller than transjunctional voltages known to induce lower conductive states (Vo>Vj). The data clearly indicated that the subconducting states occupy only a small fraction of the total channel open time. This was reflected by the fact that the average open probability for the subconductive state(s) determined from the 9 records analyzed was approximately 2%. Closer inspection of the data revealed that the frequency of subconductive states was actually higher than the frequency of the main state conductance. In summary, recording conditions sufficient for evaluation of the intrinsic gating characteristics of human Cx43-derived gap junction channels have been used. Under these conditions, our data clearly indicate that despite their greater frequency, the duration of subconductance events is so short relative to the main state duration as to render them physiologically insignificant.
Collapse
Affiliation(s)
- G J Christ
- Departments of Urology and Physiology & Biophysics, Albert Einstein College of Medicine, Bronx, NY, USA.
| | | |
Collapse
|
48
|
Chapter 3: Homotypic, Heterotypic, and Heteromeric Gap Junction Channels. CURRENT TOPICS IN MEMBRANES 1999. [DOI: 10.1016/s0070-2161(08)61007-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register]
|
49
|
Kurjiaka DT, Steele TD, Olsen MV, Burt JM. Gap junction permeability is diminished in proliferating vascular smooth muscle cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:C1674-82. [PMID: 9843730 DOI: 10.1152/ajpcell.1998.275.6.c1674] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In atherosclerosis and hypertension, vascular smooth muscle cells (SMCs) are stimulated to proliferate and exhibit enhanced gap junction protein expression. Our goal was to determine whether gap junction function differs in proliferating vs. growth-arrested SMCs. A7r5 cells (embryonic rat aortic SMCs) did not proliferate in media with reduced serum ( approximately 90% of cells in G0/G1 phase after 48-96 h in 1% fetal bovine serum). Dye coupling was less but electrical coupling was comparable in proliferating vs. growth-arrested A7r5 cells, suggesting differences in junctional permselectivity. In growth-arrested cells, junctional conductances measured with potassium glutamate, tetraethylammonium chloride, and KCl were well predicted by the conductivities of these solutions. In contrast, junctional conductances measured with potassium glutamate and tetraethylammonium chloride in proliferating cells were significantly greater than predicted by the conductivities of these solutions. These results suggest that junctions between growth-arrested cells are permeated equally well and simultaneously by anions and cations, whereas junctions between proliferating cells are poorly permeated by large molecules of either charge and equally well but not simultaneously by small anions and cations. The data indicate that A7r5 cells regulate chemical coupling independent of electrical coupling, a capacity that could facilitate growth control while protecting vasomotor responsiveness of vessels.
Collapse
Affiliation(s)
- D T Kurjiaka
- Department of Physiology, University of Arizona, Tucson, Arizona 85724, USA
| | | | | | | |
Collapse
|
50
|
Abstract
Gap junction channels are the only class of channels which span two closely apposed plasma membranes. There are over a dozen identified subunit proteins or connexins. Three generic types of gap junction channels are possible. They are the homotypic, heterotypic and heteromeric types, each of which has a distinct connexin distribution. The major connexin found in vascular smooth muscle is connexin43. Connexin40 has also been found in vascular smooth muscle. The biosynthesis, trafficking and degradation of connexin43 has only recently been studied but the data reveal some interesting features such as a short half-life of only 1.5-3.5 h. The gating characteristics of connexin43 reveal mode shifting behaviours which result in prolonged closure of the majority of the gap junction channels. The channel also displays weak voltage dependence and is poorly selective. These features suggest that dynamical regulation of cell-to-cell coupling is best designed to reduce cell-to-cell coupling, rather than enhance it, by down regulation of channel activity through the biosynthesis, trafficking, degradation pathways and gating via mode shifting.
Collapse
Affiliation(s)
- P R Brink
- Department of Physiology and Biophysics, SUNY at Stony Brook 11794, USA
| |
Collapse
|