Introduction of high molecular weight (IgG) proteins into receptor coupled, permeabilized smooth muscle

Peptide-N-glycosidase F or A treatment and procainamide-labeling for identification and quantification of N-glycans in two types of mammalian glycoproteins using UPLC and LC-MS/MS

BACKGROUND

N-glycans in glycoproteins can affect physicochemical properties of proteins; however, some reported N-glycan structures are inconsistent depending on the type of glycoprotein or the preparation methods.

OBJECTIVE

To obtain consistent results for qualitative and quantitative analyses of N-glycans, N-glycans obtained by different preparation methods were compared for two types of mammalian glycoproteins.

METHODS

N-glycans are released by peptide-N-glycosidase F (PF) or A (PA) from two model mammalian glycoproteins, bovine fetuin (with three glycosylation sites) and human IgG (with a single glycosylation site), and labeled with a fluorescent tag [2-aminobenzamide (AB) or procainamide (ProA)]. The structure and quantity of each N-glycan were determined using UPLC and LC-MS/MS.

RESULTS

The 21 N-glycans in fetuin and another 21 N-glycans in IgG by either PF-ProA or PA-ProA were identified using LC-MS/MS. The N-glycans in fetuin (8-13 N-glycans were previously reported) and in IgG (19 N-glycans were previously reported), which could not be identified by using the widely used PF-AB, were all identified by using PF-ProA or PA-ProA. The quantities (%) of the N-glycans (>0.1 %) relative to the total amount of N-glycans (100 %) obtained by AB- and ProA-labeling using LC-MS/MS had a similar tendency. However, the absolute quantities (pmol) of the N-glycans estimated using UPLC and LC-MS/MS were more efficiently determined with ProA-labeling than with AB-labeling. Thus, PF-ProA or PA-ProA allows for more effective identification and quantification of N-glycans than PF-AB in glycoprotein, particularly bovine fetuin. This study is the first comparative analysis for the identification and relative and absolute quantification of N-glycans in glycoproteins with PF-ProA and PA-ProA using UPLC and LC-MS/MS.

Differential Refractometric Biosensor for Reliable Human IgG Detection: Proof of Concept

A new sensing platform based on long-period fiber gratings (LPFGs) for direct, fast, and selective detection of human immunoglobulin G (IgG; Mw = 150 KDa) was developed and characterized. The transducer's high selectivity is based on the specific interaction of a molecularly imprinted polymer (MIPs) design for IgG detection. The sensing scheme is based on differential refractometric measurements, including a correction system based on a non-imprinted polymer (NIP)-coated LPFG, allowing reliable and more sensitive measurements, improving the rejection of false positives in around 30%. The molecular imprinted binding sites were performed on the surface of a LPFG with a sensitivity of about 130 nm/RIU and a FOM of 16 RIU^-1. The low-cost and easy to build device was tested in a working range from 1 to 100 nmol/L, revealing a limit of detection (LOD) and a sensitivity of 0.25 nmol/L (0.037 µg/mL) and 0.057 nm.L/nmol, respectively. The sensor also successfully differentiates the target analyte from the other abundant elements that are present in the human blood plasma.

Trypsin-induced elevated contractile responses in a rat model of interstitial cystitis/bladder pain syndrome: Involvement of PAR2 and intracellular Ca2+ release pathways

AIMS

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a chronic inflammatory disease with unclear etiology. Different receptors play a role in the pathophysiology including protease activated receptors (PARs). The present study aimed to investigate the subtypes and the effects of PARs on contractility using permeabilized detrusor smooth muscle strips in IC/BPS.

MAIN METHODS

IC/BPS was induced by cyclophosphamide injection. Histopathological analysis, PCR for detecting PAR proteins, western blotting for indicating PAR2 protein expression levels and myograph recording for measuring contractile force were used.

KEY FINDINGS

The present study reveals that in rat bladder PAR1 and PAR2 but not PAR4 were found to be expressed. The first evidence was revealed where trypsin-induced contractions in rat permeabilized detrusor were potentiated in CYP-induced cystitis. Moreover, the functional inhibition of trypsin-induced contractions by selective PAR2 antagonist (ENMD-1068) and the supporting immunoblotting results emphasized that the main PAR subtype involved in IC/BPS model in rat bladder is PAR2. Our data emphasize the prominent role of IP₃ in cystitis pathology besides ryanodine channels. Trypsin-induced Ca²⁺sensitization contractions were also higher in cystitis. Both Rho kinase and protein kinase C played a role in this increased Ca²⁺sensitization situation.

SIGNIFICANCE

The present paper highlights the intracellular pathways that are involved in trypsin-induced contractions mainly via PAR2 in permeabilized bladder detrusor smooth muscle in a rat model of IC/BPS.

Analysis of neuronal Ca2+ handling properties by combining perforated patch clamp recordings and the added buffer approach

Ca2+ functions as an important intracellular signal for a wide range of cellular processes. These processes are selectively activated by controlled spatiotemporal dynamics of the free cytosolic Ca2+. Intracellular Ca2+ dynamics are regulated by numerous cellular parameters. Here, we established a new way to determine neuronal Ca2+ handling properties by combining the 'added buffer' approach [1] with perforated patch-clamp recordings [2]. Since the added buffer approach typically employs the standard whole-cell configuration for concentration-controlled Ca2+ indicator loading, it only allows for the reliable estimation of the immobile fraction of intracellular Ca2+ buffers. Furthermore, crucial components of intracellular signaling pathways are being washed out during prolonged whole-cell recordings, leading to cellular deterioration. By combining the added buffer approach with perforated patch-clamp recordings, these issues are circumvented, allowing the precise quantification of the cellular Ca2+ handling properties, including immobile as well as mobile Ca2+ buffers.

Glass-like protein condensate for the long-term storage of proteins

Long-term storage of proteins at ambient temperature is required for applications in pharmaceutics and biotechnology. Lyophilization is a versatile approach for stabilizing proteins at ambient temperature, although its freezing and drying processes negatively affect the protein structure. In this study, we show a glass-like protein condensate (GLPC) as a new method for protein stabilization at ambient temperature. Various protein types, including immunoglobulin G, gamma globulin, albumin, and chymotrypsin, formed a glassy state during ultracentrifugation and natural drying, while proteins that tend to crystalize, such as hen egg-white lysozyme, did not. The GLPCs were characterized by a transparent solid state, similar to a dry glass ball. Importantly, the GLPCs were dissolved easily in saline solution at a physiological concentration, thereby retaining their native structures and functions. The GLPCs preserved their native structures even after 1 year of incubation at ambient temperature. These results provide a framework for the development of protein preservation methods at ambient temperature other than lyophilization.

Repeated dose multi-drug testing using a microfluidic chip-based coculture of human liver and kidney proximal tubules equivalents

A microfluidic multi-organ chip emulates the tissue culture microenvironment, enables interconnection of organ equivalents and overcomes interspecies differences, making this technology a promising and powerful tool for preclinical drug screening. In this study, we established a microfluidic chip-based model that enabled non-contact cocultivation of liver spheroids and renal proximal tubule barriers in a connecting media circuit over 16 days. Meanwhile, a 14-day repeated-dose systemic administration of cyclosporine A (CsA) alone or in combination with rifampicin was performed. Toxicity profiles of the two different doses of CsA on different target organs could be discriminated and that concomitant treatment with rifampicin from day6 onwards decreased the CsA concentration and attenuated the toxicity compared with that after treatment with CsA for 14 consecutive days. The latter is manifested with the changes in cytotoxicity, cell viability and apoptosis, gene expression of metabolic enzymes and transporters, and noninvasive toxicity biomarkers. The on chip coculture of the liver and the proximal tubulus equivalents showed its potential as an effective and translational tool for repeated dose multi-drug toxicity screening in the preclinical stage of drug development.

The dominant protein phosphatase PP1c isoform in smooth muscle cells, PP1cβ, is essential for smooth muscle contraction

Contractile force development of smooth muscle is controlled by balanced kinase and phosphatase activities toward the myosin regulatory light chain (RLC). Numerous biochemical and pharmacological studies have investigated the specificity and regulatory activity of smooth muscle myosin light-chain phosphatase (MLCP) bound to myosin filaments and comprised of the regulatory myosin phosphatase target subunit 1 (MYPT1) and catalytic protein phosphatase 1cβ (PP1cβ) subunits. Recent physiological and biochemical evidence obtained with smooth muscle tissues from a conditional MYPT1 knockout suggests that a soluble, MYPT1-unbound form of PP1cβ may additionally contribute to myosin RLC dephosphorylation and relaxation of smooth muscle. Using a combination of isoelectric focusing and isoform-specific immunoblotting, we found here that more than 90% of the total PP1c in mouse smooth muscles is the β isoform. Moreover, conditional knockout of PP1cα or PP1cγ in adult smooth muscles did not result in an apparent phenotype in mice up to 6 months of age and did not affect smooth muscle contractions ex vivo In contrast, smooth muscle-specific conditional PP1cβ knockout decreased contractile force development in bladder, ileal, and aortic tissues and reduced mouse survival. Bladder smooth muscle tissue from WT mice was selectively permeabilized to remove soluble PP1cβ to measure contributions of total (α-toxin treatment) and myosin-bound (Triton X-100 treatment) phosphatase activities toward phosphorylated RLC in myofilaments. Triton X-100 reduced PP1cβ content by 60% and the rate of RLC dephosphorylation by 2-fold. These results are consistent with the selective dephosphorylation of RLC by both MYPT1-bound and -unbound PP1cβ forms in smooth muscle.

Rho Kinase and Protein Kinase C Pathways are Responsible for Enhanced Carbachol Contraction in Permeabilized Detrusor in a Rat Model of Cystitis

Interstitial cystitis is a syndrome characterized by detrusor overactivity and chronic inflammation of the bladder. The mechanisms responsible for the altered smooth muscle contractility remain poorly understood. The aim of the study was to investigate the role of intracellular signalling pathways in carbachol-induced detrusor contraction in a rat model of interstitial cystitis. Cyclophosphamide (150 mg/kg, dissolved in saline) was injected to rats (Sprague-Dawley, female, 200-250 g) intraperitoneally once a day on days 1, 4 and 7 to induce interstitial cystitis. Control groups were injected with saline (0.9% NaCl). Detrusor smooth muscle strips were mounted in 1-ml organ baths containing HEPES-buffered modified Krebs' solution and permeabilized with 40 μM β-escin for 30 min. Carbachol-induced contractions were significantly increased from 21.2 ± 1.6% (saline-treated) to 44 ± 4.4% in cyclophosphamide-treated group. The Rho kinase inhibitor Y-27632 (8.8 ± 2%) and the protein kinase C inhibitor GF-109203X (11.7 ± 2.8%) inhibited the increased contractile response (44 ± 4.4%) in rats with cystitis. The increased carbachol-induced contraction (44 ± 4.4%) was also significantly inhibited by the sarcoplasmic reticulum ryanodine channel blocker ryanodine (25.8 ± 3.2%) and the sarcoplasmic reticulum IP₃ receptor blocker heparin (17.2 ± 2.2%) in cystitis. RhoA protein levels in the bladder of cyclophosphamide-treated rats were significantly increased while pan-protein kinase C (α, β and γ isoforms) protein expression was unaltered between experimental groups. Carbachol-induced calcium sensitization at constant and clamped calcium (pCa 6) was also increased in cystitis (from 15.8 ± 2.2% to 24.7 ± 2.8%). This increased response (24.7 ± 2.8%) was significantly inhibited by both Y-27632 (7.9 ± 0.7%) and GF-109203X (4.4 ± 1.5%). We conclude that interstitial cystitis is characterized by an enhanced carbachol contractile response as well as by calcium sensitization of the detrusor smooth muscle. Activation of Rho kinase and protein kinase C pathways may be the molecular culprits responsible for the augmented muscarinic response observed in cystitis.

Purification of antibody against Ara h 2 by a homemade immunoaffinity chromatography column

Antibodies are used extensively in numerous applications both in vivo and in vitro. To purify anti-Ara h 2 polyclonal antibody, a homemade immunoaffinity chromatography (IAC) column method was established. The properties of homemade column were compared with those of the mAb affinity protein G (MPG) agarose high flow, a commercially available column successfully used in capturing polyclonal antibodies. During antibody purification from rabbits' antiserum against Ara h 2, the column capacity, recovery, and purification factor were characterized for IAC and MPG. The homemade IAC could separate the corresponding antibody with higher specificity and lower cost but with lower recovery and column capacity than those of MPG. Thus, the homemade IAC is a specific, inexpensive, and suitable method that can be used for various laboratory purifications.

Direct Evidence for Daily Plasticity of Electrical Coupling between Rod Photoreceptors in the Mammalian Retina

Rod photoreceptors are electrically coupled through gap junctions. Coupling is a key determinant of their light response properties, but whether rod electrical coupling is dynamically regulated remains elusive and controversial. Here, we have obtained direct measurements of the conductance between adjacent rods in mouse retina and present evidence that rod electrical coupling strength is dependent on the time of day, the lighting conditions, and the mouse strain. Specifically, we show in CBA/Ca mice that under circadian conditions, the rod junctional conductance has a median value of 98 pS during the subjective day and of 493 pS during the subjective night. In C57BL/6 mice, the median junctional conductance between dark-adapted rods is ∼140 pS, regardless of the time in the circadian cycle. Adaptation to bright light decreases the rod junctional conductance to ∼0 pS, regardless of the time of day or the mouse strain. Together, these results establish the high degree of plasticity of rod electrical coupling over the course of the day. Estimates of the rod coupling strength will provide a foundation for further investigations of rod interactions and the role of rod coupling in the ability of the visual system to anticipate, assimilate, and respond to the daily changes in ambient light intensity.

SIGNIFICANCE STATEMENT

Many cells in the CNS communicate via gap junctions, or electrical synapses, the regulation of which remains largely unknown. Here, we show that the strength of electrical coupling between rod photoreceptors of the retina is regulated by the time of day and the lighting conditions. This mechanism may help us understand some key aspects of day and night vision as well as some visual malfunctions.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Aging changes agonist induced contractile responses in permeabilized rat bladder

Aging alters bladder functions where a decrease in filling, storage and emptying is observed. These changes cause urinary incontinence, especially in women. The aim of this study is to examine how aging affects the intracellular calcium movements due to agonist-induced contractions in permeabilized female rat bladder. Urinary bladder isolated from young and old female Sprague-Dawley rats were used. Small detrusor strips were permeabilized with β-escin. The contractile responses induced with agonists were compared between young and old groups. Carbachol-induced contractions were decreased in permeabilized detrusor from old rats compared to young group. Heparin and ryanodine decreased carbachol-induced contractions in young rats where only heparin inhibited these contractions in olds. Caffeine-induced contractions but not inositol triphosphate (IP3)-induced contractions were decreased in old group compared to youngs. The cumulative calcium response curves (pCa 8-4) were also decreased in old rats. Carbachol-induced calcium sensitization responses did not alter by age where GTP-β-S and GF-109203X but not Y-27632 inhibited these responses. Carbachol-induced contractions decrease with aging in rat bladder detrusor. It can be postulated as IP3-induced calcium release (IICR) is primarily responsible for the contractions in older rats where the decrease in carbachol contractions in aging may be as a result of a decrease in calcium-induced calcium release (CICR), rather than carbachol-induced calcium sensitization.

Hydrogen sulphide inhibits carbachol-induced contractile responses in β-escin permeabilized guinea-pig taenia caecum

Hydrogen sulphide (H(2)S) is an endogenous mediator producing a potent relaxation response in vascular and non-vascular smooth muscles. While ATP-sensitive potassium channels are mainly involved in this relaxant effect in vascular smooth muscle, the mechanism in other smooth muscles has not been revealed yet. In the present study, we investigated how H(2)S relaxes non-vascular smooth muscle by using intact and β-escin permeabilized guinea-pig taenia caecum. In intact tissues, concentration-dependent relaxation response to H(2)S donor NaHS in carbachol-precontracted preparations did not change in the presence of a K(ATP) channel blocker glibenclamide, adenylate cyclase inhibitor SQ-22536, guanylate cyclase inhibitor ODQ, protein kinase A inhibitor KT-5720, protein kinase C inhibitor H-7, tetrodotoxin, apamin/charybdotoxin, NOS inhibitor L-NAME and cyclooxygenase inhibitor indomethacin. We then studied how H(2)S affected carbachol- or Ca(2+)-induced contractions in permeabilized tissues. When Ca(2+) was clamped to a constant value (pCa6), a further contraction could be elicited by carbachol that was decreased by NaHS. This decrease in contraction was reversed by catalase but not by superoxide dismutase or N-acetyl cysteine. The sarcoplasmic reticulum Ca(2+)-ATPase pump inhibitor, cyclopiazonic acid, also decreased the carbachol-induced contraction that was further inhibited by NaHS. Mitochondrial proton pump inhibitor carbonyl cyanide p-trifluromethoxyphenylhydrazone also decreased the carbachol-induced contraction but this was not additionally changed by NaHS. The carbachol-induced Ca(2+) sensitization, calcium concentration-response curves, IP(3)- and caffeine-induced contractions were not affected by NaHS. In conclusion, we propose that hydrogen peroxide and mitochondria may have a role in H(2)S-induced relaxation response in taenia caecum.

On the mechanism of autoinhibition of the RhoA-specific nucleotide exchange factor PDZRhoGEF

Background

The Dbl-family of guanine nucleotide exchange factors (GEFs) activate the cytosolic GTPases of the Rho family by enhancing the rate of exchange of GTP for GDP on the cognate GTPase. This catalytic activity resides in the DH (Dbl-homology) domain, but typically GEFs are multidomain proteins containing other modules. It is believed that GEFs are autoinhibited in the cytosol due to supramodular architecture, and become activated in diverse signaling pathways through conformational change and exposure of the DH domain, as the protein is translocated to the membrane. A small family of RhoA-specific GEFs, containing the RGSL (regulators of G-protein signaling-like) domain, act as effectors of select GPCRs via Gα_12/13, although the molecular mechanism by which this pathway operates is not known. These GEFs include p115, LARG and PDZRhoGEF (PRG).

Results

Here we show that the autoinhibition of PRG is caused largely by an interaction of a short negatively charged sequence motif, immediately upstream of the DH-domain and including residues Asp706, Glu708, Glu710 and Asp712, with a patch on the catalytic surface of the DH-domain including Arg867 and Arg868. In the absence of both PDZ and RGSL domains, the DH-PH tandem with additional 21 residues upstream, is 50% autoinhibited. However, within the full-length protein, the PDZ and/or RGSL domains significantly restore autoinhibition.

Conclusion

Our results suggest a mechanism for autoinhibition of RGSL family of GEFs, in which the RGSL domain and a unique sequence motif upstream of the DH domain, act cooperatively to reduce the ability of the DH domain to bind the nucleotide free RhoA. The activation mechanism is likely to involve two independent steps, i.e. displacement of the RGSL domain and conformational change involving the autoinhibitory sequence motif containing several negatively charged residues.

Gap junction channels exhibit connexin-specific permeability to cyclic nucleotides

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.

Calcium sensitivity and cooperativity of permeabilized rat mesenteric lymphatics

Lymphatic muscle contraction is critical for the centripetal movement of lymph that regulates fluid balance, protein homeostasis, lipid absorption, and immune function. We have demonstrated that lymphatic muscle has both smooth and striated muscle contractile elements; however, the basic contractile properties of this tissue remain poorly defined. We hypothesized that contractile characteristics of lymphatic myofilaments would be different from vascular smooth muscle myofilaments. To test this hypothesis, -log[Ca(2+)] (pCa)-tension relationship was determined for alpha-toxin permeabilized mesenteric lymphatics, arteries, and veins. The Ca(2+) sensitivity (pCa(50)) of mesenteric lymphatics was significantly lower compared with arteries (6.16 +/- 0.05 vs. 6.44 +/- 0.02; P < 0.05), whereas there was no difference in pCa(50) between lymphatics and veins (6.16 +/- 0.05 vs. 6.00 +/- 0.10; not significant). The Hill coefficient for alpha-toxin-permeabilized lymphatics was not significantly different from arteries but was significantly greater than that of the veins (1.98 +/- 0.19 vs. 1.21 +/- 0.18; P < 0.05). In addition, the maximal tension and pCa(50) values were significantly greater in alpha-toxin-permeabilized lymphatics compared with beta-escin-permeabilized lymphatics (0.27 +/- 0.03 vs. 0.15 +/- 0.01 and 6.16 +/- 0.05 vs. 5.86 +/- 0.06 mN/mm, respectively; P < 0.05), whereas the Hill coefficient was significantly greater in beta-escin-permeabilized lymphatics. Western blot analyses revealed that CPI-17 levels were significantly decreased by about 50% in beta-escin-permeabilized lymphatics, compared with controls, whereas no change in the level of calmodulin was detected. Our data constitute the first description of the pCa-tension relationship in permeabilized lymphatic muscle. It suggests that differences in myofilament Ca(2+) sensitivity and cooperativity among lymphatic muscle and vascular smooth muscles contribute to the functional differences that exist between these tissues.

Involvement of Rho kinase and protein kinase C in carbachol-induced calcium sensitization in beta-escin skinned rat and guinea-pig bladders

1. The signal transduction pathways involved in carbachol (CCh)-induced calcium sensitization in beta-escin permeabilized rat and guinea-pig bladder smooth muscles were investigated and the results were compared with guinea-pig taenia caecum. 2. Calcium contractions elicited cumulatively (pCa 7.5-5) in the presence of calmodulin were significantly increased in all three tissues when CCh (50 microM) was added to the medium. 3. Under constant [Ca2+]i conditions (pCa 6), calmodulin (1 microM) and then GTP (100 microM) initiated significant contractions. CCh (50 microM) added to the bath caused a further contraction in all three tissues - calcium sensitization. This sensitization was significantly inhibited by atropine (50 microM). 4. The incubation of the tissues with the IP3-receptor blocker 2-APB (30 microM) reduced the subsequent development of calcium sensitization by CCh in rat bladder but did not affect it in guinea-pig bladder and taenia ceacum. 5. The Rho kinase (ROK) inhibitor Y-27632 (5 microM) added in the presence of CCh reversed the calcium sensitization in rat bladder, whereas a transient contraction followed by a relaxation to a level not significantly different from the CCh contraction was seen in both guinea-pig bladder and taenia caecum. Y-27632 (1 microM) continuously present significantly inhibited the CCh-induced Ca2+ sensitization in rat bladder but not in guinea-pig bladder or taenia caecum. 6. In the presence of cyclopiazonic acid (CPA) (1 microM) and calmodulin (1 microM), Y-27632 (5 microM) did not change the calcium response curve (3 x 10(-7)-10(-5) M) in rat bladder but increased the contractile responses significantly in both guinea-pig bladder and taenia caecum. 7. The protein kinase C (PKC) inhibitor GF 109203X (5 microM) added in the presence of CCh inhibited the calcium sensitization induced by this muscarinic agonist in all three tissues in different ratios. 8. In conclusion, muscarinic receptor activation induces calcium sensitization in rat and guinea-pig detrusor smooth muscles but there are differences in their pathways.

Effects of radial shock waves on membrane permeability and viability of chondrocytes and structure of articular cartilage in equine cartilage explants

OBJECTIVE

To investigate in vitro effects of radial shock waves on membrane permeability, viability, and structure of chondrocytes and articular cartilage.

SAMPLE POPULATION

Cartilage explants obtained from the third metacarpal and metatarsal bones of 6 horses.

PROCEDURE

Equine cartilage was subjected to radial shock waves and then maintained as explants in culture for 48 hours. Treatment groups consisted of a negative control group; application of 500, 2,000, and 4,000 impulses by use of a convex handpiece (group A); and application of 500, 2,000, and 4,000 impulses by use of a concave handpiece (group B). Effects on explant structure were evaluated by use of environmental scanning electron microscopy (ESEM). Membrane permeability was determined by release of lactate dehydrogenase (LDH). Chondrocyte viability was assessed by use of vital cell staining. Comparisons of LDH activity and nonviable cell percentages were performed by ANOVA.

RESULTS

Cell membrane permeability increased significantly after application of 2,000 and 4,000 impulses in groups A and B. A significant decrease in cell viability was observed for application of 4,000 impulses in explants of group A. There was no detectable damage to integrity of cartilage explants observed in any treatment group by use of ESEM.

CONCLUSIONS AND CLINICAL RELEVANCE

Radial shock waves do not appear to structurally damage articular cartilage but do impact chondrocyte viability and membrane permeability. Caution should be exercised when extremely high periarticular pulse doses are used until additional studies can determine the long-term outcome of these effects and appropriate periarticular treatment regimens can be validated.

Beta-escin diminishes voltage-gated calcium current rundown in perforated patch-clamp recordings from rat primary afferent neurons

Perforated patch recordings of neuronal calcium currents (I(Ca)) with amphotericin B or nystatin reduce dialysis of intracellular constituents and current rundown, but can be difficult and frequently unsuccessful. We investigated the saponin beta-escin as a putative ionophore for perforated patch I(Ca) recordings in acutely dissociated, rat dorsal root ganglion neurons. I(Ca) was recorded in time-course studies after including either beta-escin (50 microM), or amphotericin B (240 microg/ml) as perforating ionophores in the internal pipette solution, in comparison to standard ruptured-patch technique, using suction. Perforated patches were allowed to take place spontaneously. The percentage loss of I(Ca) per min (within the first 20 min) was significantly less after beta-escin (0.0518%) (n = 18), versus either amphotericin (1.82%) (n = 12) or standard patch (4.52%) (n = 7), (P < 0.001). The slope of the rundown after linear fit was also less after beta-escin (P < 0.001). Minimal "steady-state" access resistance (R(a)) of 6.6 +/- 1.6 MOmega was achieved within 7.1 +/- 9.3 min following perforation with beta-escin, 7.9 +/- 3.5 MOmega within 44 =/- 14 min after amphotericin B, and 6.8 +/- 1.9 MOmega with standard patch (P < 0.05 for R(a), and P < 0.01 for permeabilization time, respectively). Success rates were 59% with beta-escin versus 27% with amphotericin. Leak >10% of peak I(Ca) was present in 25% of cells after beta-escin versus 20% after amphotericin, and 12% after standard technique. Perforated patches using beta-escin were stable for 15-60 min. We conclude that beta-escin may be used as an alternative ionophore for perforated patch-clamp studies in neurons, and results in minimal rundown that can facilitate long-term recordings of I(Ca). Limited rundown may be due to better preservation of cytosolic ATP content.

8-Bromo-cAMP decreases the Ca2+ sensitivity of airway smooth muscle contraction through a mechanism distinct from inhibition of Rho-kinase

To clarify whether cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA) activation and Rho-kinase inhibition share a common mechanism to decrease the Ca2+ sensitivity of airway smooth muscle contraction, we examined the effects of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP), a stable cAMP analog, and (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a Rho-kinase inhibitor, on carbachol (CCh)-, guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-, 4beta-phorbol 12,13-dibutyrate (PDBu)-, and leukotriene D4 (LTD4)-induced Ca2+ sensitization in alpha-toxin-permeabilized rabbit tracheal and human bronchial smooth muscle. In rabbit trachea, CCh-induced smooth muscle contraction was inhibited by 8-BrcAMP and Y-27632 to a similar extent. However, GTPgammaS-induced smooth muscle contraction was resistant to 8-BrcAMP. In the presence of a saturating concentration of Y-27632, PDBu-induced smooth muscle contraction was completely reversed by 8-BrcAMP. Conversely, PDBu-induced smooth muscle contraction was resistant to Y-27632. In the presence of a saturating concentration of 8-BrcAMP, GTPgammaS-induced Ca2+ sensitization was also reversed by Y-27632. The 8-BrcAMP had no effect on the ATP-triggered contraction of tracheal smooth muscle that had been treated with calyculin A in rigor solutions. The 8-BrcAMP and Y-27632 additively accelerated the relaxation rate of PDBu- and GTPgammaS-treated smooth muscle under myosin light chain kinase-inhibited conditions. In human bronchus, LTD4-induced smooth muscle contraction was inhibited by both 8-BrcAMP and Y-27632. We conclude that cAMP/PKA-induced Ca2+ desensitization contains at least two mechanisms: 1) inhibition of the muscarinic receptor signaling upstream from Rho activation and 2) cAMP/PKA's preferential reversal of PKC-mediated Ca2+ sensitization in airway smooth muscle.

Up-regulation of Rnd1 during pregnancy serves as a negative-feedback control for Ca2+ sensitization of contractile elements in rat myometrium

We investigated the role of Rnd1, a member of the small GTP-binding Rho protein family, in the change in Ca(2+) sensitivity of contractile element in rat myometrium at estrus, gestation, and postpartum stages. In the permeabilized muscles, GTPgammaS or carbachol with GTP increased Ca(2+) sensitivity of contractile force in non-pregnant myometrium at the estrus stage, whereas these stimuli were ineffective in pregnant myometrium at day 21. After postpartum, the reduced Ca(2+) sensitization was recovered. Semi-quantitative RT-PCR analysis indicated that the expressions of RhoA, ROCKI, and ROCKII were not significantly different between non-pregnant and pregnant myometria. In contrast, the expression of Rnd1 was increased during the course of pregnancy, reaching a maximal at day 21, and rapidly declined after the delivery. On the other hand, Ca(2+) sensitization of contractile elements was decreased during the progress in gestation. These results suggest that Rnd1 may have an important role as a negative-feedback control of uterine contraction during gestation through the inhibition of RhoA-mediated increase in the Ca(2+) sensitivity of contractile elements.

Extraction and reconstitution of calponin and consequent contractile ability in permeabilized smooth muscle fibers

We demonstrate reduction and restoration of contractile ability in response to protein extraction and reconstitution in Triton X-100/glycerol-permeabilized smooth muscle fibers. Through significant reduction in the content of caldesmon (CaD), calponin (CaP), and the 20-kDa regulatory light chain (RLC) of myosin, but not other contractile proteins in "chemically skinned" fibers, we substantially reduced the contractile ability of these fibers, as measured by their ability to generate isometric force and to hydrolyze ATP by actomyosin Mg2+ ATPase. When the protein-depleted fibers were then reconstituted (either with a mixture of purified protein standards of CaD, CaP, and myosin RLC or with a protein extract from the demembranized muscle fibers containing CaD, CaP, and myosin RLC plus several low-molecular-mass proteins), all proteins used for reincorporation returned nearly to control levels, as did isometric force generation and rate of ATP hydrolysis. The fact that the low-molecular-mass proteins do not affect contractility in this model system indicates that our methods for reversible modulation of the content of CaP and CaD may provide a valuable tool for studying the thin-filament-based regulation of contractility.

Receptor-independent activation of Rho-kinase-mediated calcium sensitisation in smooth muscle

1. The aim of this work was to determine whether Rho-kinase-mediated calcium sensitisation contributes to contractions of the mouse anococcygeus smooth muscle and, if so, whether the process was activated by receptor-dependent or receptor-independent mechanisms. 2. The Rho-kinase inhibitor Y27632 produced concentration-dependent decreases in tone raised by either the muscarinic receptor agonist carbachol (CCh), or the sarco-endoplasmic reticulum calcium ATPase inhibitor thapsigargin (Tg) (EC(50) values against CCh and Tg of 8.4+/-3.3 (n=6) and 6.1+/-2.1 (n=7) micro M, respectively). Pretreatment of tissues with Y27632 also inhibited contractions produced by 65 mM external potassium (69+/-7% (n=4) inhibition using 10 micro M Y27632). Y27632 had no effect on contractions produced by the inhibitor of smooth muscle myosin light-chain phosphatase, calyculin-A. 3. In beta-escin-permeabilised preparations, both CCh and Tg produced significant increases in tone over-and-above that produced by a combination of calcium (1 micro M) and GTP (100 micro M). These responses to CCh and Tg were inhibited by Y27632 (10 micro M). 4. Western blot analysis of fractionated tissue samples probed for RhoA immunoreactivity, indicated that both CCh and Tg were able to induce translocation of RhoA from the cytosol to the membrane. 5. These findings suggest that Rho-kinase-mediated calcium sensitisation is activated by both receptor-dependent and receptor-independent mechanisms in the mouse anococcygeus.

Sphingosylphosphorylcholine is a novel messenger for Rho-kinase-mediated Ca2+ sensitization in the bovine cerebral artery: unimportant role for protein kinase C

Although recent investigations have suggested that a Rho-kinase-mediated Ca2+ sensitization of vascular smooth muscle contraction plays a critical role in the pathogenesis of cerebral and coronary vasospasm, the upstream of this signal transduction has not been elucidated. In addition, the involvement of protein kinase C (PKC) may also be related to cerebral vasospasm. We recently reported that sphingosylphosphorylcholine (SPC), a sphingolipid, induces Rho-kinase-mediated Ca2+ sensitization in pig coronary arteries. The purpose of this present study was to examine the possible mediation of SPC in Ca2+ sensitization of the bovine middle cerebral artery (MCA) and the relation to signal transduction pathways mediated by Rho-kinase and PKC. In intact MCA, SPC induced a concentration-dependent (EC50=3.0 micromol/L) contraction, without [Ca2+]i elevation. In membrane-permeabilized MCA, SPC induced Ca2+ sensitization even in the absence of added GTP, which is required for activation of G-proteins coupled to membrane receptors. The SPC-induced Ca2+ sensitization was blocked by a Rho-kinase inhibitor (Y-27632) and a dominant-negative Rho-kinase, but not by a pseudosubstrate peptide for conventional PKC, which abolished the Ca2+-independent contraction induced by phorbol ester. In contrast, phorbol ester-induced Ca2+ sensitization was resistant to a Rho-kinase inhibitor and a dominant-negative Rho-kinase. In primary cultured vascular smooth muscle cells, SPC induced the translocation of cytosolic Rho-kinase to the cell membrane. We propose that SPC is a novel messenger for Rho-kinase-mediated Ca2+ sensitization of cerebral arterial smooth muscle and, therefore, may play a pivotal role in the pathogenesis of abnormal contraction of the cerebral artery such as vasospasm. The SPC/Rho-kinase pathway functions independently of the PKC pathway.

Extensive skinning of cell membrane diminishes the force-inhibiting effect of okadaic acid on smooth muscles of Guinea pig hepatic portal vein

The influences of cell membrane permeabilization (skinning) on the okadaic acid-induced inhibition of vascular smooth muscle contraction were studied in guinea pig hepatic portal vein. Pretreatment by 1 microM okadaic acid in the absence of Ca(2+) suppressed subsequent submaximal Ca(2+)-induced contraction in preparations permeabilized with Staphylococcus aureus alpha-toxin or beta-escin, but not in those treated with saponin or Triton X-100. The SDS-PAGE of elutants from the preparation suggests that the loss of the inhibitory effect of okadaic acid in preparations skinned with saponin or Triton X-100 results from the leakage of some cellular components with a molecular mass of 67 to 200 kDa.

Regulation by GDI of RhoA/Rho-kinase-induced Ca2+ sensitization of smooth muscle myosin II

We characterized the role of guanine nucleotide dissociation inhibitor (GDI) in RhoA/Rho-kinase-mediated Ca2+ sensitization of smooth muscle. Endogenous contents (approximately 2-4 microM) of RhoA and RhoGDI were near stoichiometric, whereas a supraphysiological GDI concentration was required to relax Ca2+ sensitization of force by GTP and guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS). GDI also inhibited Ca2+ sensitization by GTP. G14V RhoA, by alpha-adrenergic and muscarinic agonists, and extracted RhoA from membranes. GTPgammaS translocated Rho-kinase to a Triton X-114-extractable membrane fraction. GTP. G14V RhoA complexed with GDI also induced Ca2+ sensitization, probably through in vivo dissociation of GTP. RhoA from the complex, because it was reversed by addition of excess GDI. GDI did not inhibit Ca2+ sensitization by phorbol ester. Constitutively active Cdc42 and Rac1 inhibited Ca2+ sensitization by GTP. G14V RhoA. We conclude that 1) the most likely in vivo function of GDI is to prevent perpetual "recycling" of GDP. RhoA to GTP. RhoA; 2) nucleotide exchange (GTP for GDP) on complexed GDP. RhoA/GDI can precede translocation of RhoA to the membrane; 3) activation of Rho-kinase exposes a hydrophobic domain; and 4) Cdc42 and Rac1 can inhibit Ca2+ sensitization by activated GTP. RhoA.

Inhibition of capacitative calcium entry is not obligatory for relaxation of the mouse anococcygeus by the NO/cyclic GMP signalling pathway

1. The object of this study was to determine whether inhibition of capacitative calcium entry is essential for relaxation of the mouse anococcygeus via the NO/cyclic GMP signalling pathway. 2. In intact muscles, thapsigargin (Tg; 100 nM)-induced tone was relaxed by NO, sodium nitroprusside (SNP), 8-Br-cyclic GMP, and nitrergic field stimulation. The relaxations were similar in magnitude to those observed against carbachol (50 microM) tone and, with the exception of those to 8-Br-cyclic GMP, were reduced by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxodiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 microM). 3. In single smooth muscle cells, loaded with Fura-2, both carbachol and Tg produced sustained elevations in cytoplasmic calcium levels ([Ca2+]i). SNP inhibited the rise in [Ca2+]i produced by carbachol, an effect attenuated by ODQ. In contrast, neither SNP nor 8-Br-cyclic GMP reduced the elevated [Ca2+]i associated with Tg. 4. In beta-escin skinned preparations, NO had no effect on tone induced by calcium (1 microM in the presence of 100 microM GTP). Carbachol and Tg produced further increases in calcium/GTP-induced tone and, in both cases, this additional tone was relaxed by NO and 8-Br-cyclic GMP. 5. The results support the hypothesis that the NO/cyclic GMP pathway inhibits capacitative calcium entry by refilling the internal stores, since reduction in [Ca2+]i was not observed in the presence of Tg. However, as muscle relaxation was still observed, impairment of capacitative calcium entry cannot be considered obligatory for relaxation. Results from skinned tissues suggest that inhibition of calcium sensitization processes, perhaps associated with store-depletion, may be an important mechanism of NO/cyclic GMP-induced relaxation.

Membrane permeabilization induced by discodermin A, a novel marine bioactive peptide

The effects of discodermin A (DC-A), a novel marine bioactive peptide extracted from sea sponge Discodermia kiiensis, on the vascular smooth muscle cells and tissues were examined. Analysis with a confocal laser microscope showed that DC-A (0.1-30 microM) permeabilized the plasma membrane of A10 cells to the non-permeable fluorescent agents, ethidium homodimer-1 (MW = 857) and calcein (MW = 623), in a concentration-dependent manner. In the vascular tissue treated with 30 microM DC-A, addition of a micromolar concentration of Ca(2+) evoked a sustained contraction in the presence of ATP, suggesting that DC-A increased the permeability of the membrane to Ca(2+) and ATP. DC-A at higher concentrations (30 microM) significantly increased the leakage of lactate dehydrogenase (140 kD) from the vascular tissue. These results suggest that DC-A has a permeabilizing effect on the plasma membrane possibly by interacting with plasma membrane phospholipids with its six successive hydrophobic amino acid residues at N-terminal.

Species- and temperature-dependency of the decrease in myofilament Ca2+ sensitivity induced by beta-adrenergic stimulation

Although beta-adrenergic stimulation has been shown in many studies to decrease myofilament Ca2+ sensitivity in various types of cardiac muscle such as rat and rabbit ventricles, other studies disagree with this conclusion. In the present study, we aimed to explain these contradictory findings. We examined the effect of beta-adrenoceptor stimulation on Ca2+ sensitivity using guinea pig and rat ventricles. We performed the experiment at two different temperatures and compared the results. In guinea pig ventricles, isoproterenol and forskolin did not alter the relationship between [Ca2+]i and muscle force during the relaxation phase of tetanic contraction at either 24 degrees C or 30 degrees C. In rat ventricles, in contrast, isoproterenol shifted the [Ca2+]i-force curve to the right at 24 degrees C, but not at 30 degrees C. In guinea pig ventricles permeabilized by alpha-toxin, in which the cAMP/PK-A system is intact, the addition of cAMP did not decrease Ca2+ sensitivity. These results suggest that there are species- and temperature-dependent differences in the regulation of myofilament Ca2+ sensitivity by beta-adrenergic stimulation.

Sphingosylphosphorylcholine induces Ca(2+)-sensitization of vascular smooth muscle contraction: possible involvement of rho-kinase

Sphingosylphosphorylcholine (SPC), a sphingolipid, concentration-dependently (1-50 microM) induced contraction and slight elevation of the cytosolic Ca(2+) concentration ([Ca(2+)](i)) in smooth muscle of the pig coronary artery, the result being a marked increase in the force/[Ca(2+)](i) ratio. In alpha-toxin- or beta-escin-permeabilized, but not Triton X-100-permeabilized, vascular strips, SPC induced contraction at constant [Ca(2+)](i) (pCa 6.3) in the absence of GTP, whereas a G-protein-coupled receptor agonist, histamine, required the presence of GTP to induce the contraction. The Rho-kinase blocker, Y-27632 (10 microM) abolished the SPC-induced Ca(2+)-sensitization, without affecting the Ca(2+)-induced contraction. These results suggest that SPC induces Ca(2+)-sensitization of force in vascular smooth muscle, presumably through the activation of Rho-kinase (or a related kinase).

Sorting of metabolic pathway flux by the plasma membrane in cerebrovascular smooth muscle cells

We used beta-escin-permeabilized pig cerebral microvessels (PCMV) to study the organization of carbohydrate metabolism in the cytoplasm of vascular smooth muscle (VSM) cells. We have previously demonstrated (Lloyd PG and Hardin CD. Am J Physiol Cell Physiol 277: C1250-C1262, 1999) that intact PCMV metabolize the glycolytic intermediate [1-(13)C]fructose 1,6-bisphosphate (FBP) to [1-(13)C]glucose with negligible production of [3-(13)C]lactate, while simultaneously metabolizing [2-(13)C]glucose to [2-(13)C]lactate. Thus gluconeogenic and glycolytic intermediates do not mix freely in intact VSM cells (compartmentation). Permeabilized PCMV retained the ability to metabolize [2-(13)C]glucose to [2-(13)C]lactate and to metabolize [1-(13)C]FBP to [1-(13)C]glucose. The continued existence of glycolytic and gluconeogenic activity in permeabilized cells suggests that the intermediates of these pathways are channeled (directly transferred) between enzymes. Both glycolytic and gluconeogenic flux in permeabilized PCMV were sensitive to the presence of exogenous ATP and NAD. It was most interesting that a major product of [1-(13)C]FBP metabolism in permeabilized PCMV was [3-(13)C]lactate, in direct contrast to our previous findings in intact PCMV. Thus disruption of the plasma membrane altered the distribution of substrates between the glycolytic and gluconeogenic pathways. These data suggest that organization of the plasma membrane into distinct microdomains plays an important role in sorting intermediates between the glycolytic and gluconeogenic pathways in intact cells.

A major role for the rho-associated coiled coil forming protein kinase in G-protein-mediated Ca2+ sensitization through inhibition of myosin phosphatase in rabbit trachea

1 G protein-mediated Ca2+ sensitization of airway smooth muscle contraction was investigated with respect to the relative importance of Rho-associated coiled coil forming protein kinase (ROCK) and protein kinase C (PKC). We examined the effects of Y-27632, a ROCK inhibitor, and GF 109203X, a PKC inhibitor, on guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS)-induced contraction in alpha-toxin- or beta-escin-permeabilized rabbit trachea. 2 Although pre-treatment with Y-27632 dose-dependently inhibited GTPgammaS (10 microM)-induced Ca2+ sensitization of alpha-toxin-permeabilized trachea, a Y-27632-insensitive component (approximately 16% of the maximum contraction) was retained during the early phase of the GTPgammaS response in the presence of Y-27632 (100 microM). 3 GF 109203X (5 microM) abolished 1 microM 4beta-phorbol 12, 13-dibutyrate (PDBu)-induced, but only partially inhibited the GTPgammaS-induced Ca2+ sensitization. A combination of Y-27632 (100 microM) and GF 109203X (5 microM) totally abolished the GTPgammaS response. 4 GTPgammaS caused only a small contraction in the absence of Ca2+. Wortmannin (30 microM), a myosin light chain kinase (MLCK) inhibitor, completely inhibited Ca2+-induced contraction. ATP-triggered contraction of the strip which had been treated with calyculin A (1 microM), a phosphatase inhibitor, in rigor solutions was markedly slowed by worthmannin (30 microM), but not by Y-27632 (100 microM), in the presence of GTPgammaS and Ca2+. 5 GTPgammaS, but not PDBu, contracted the beta-escin-permeabilized trachea in the absence of Ca2+, but the presence of Ca2+-independent MLCK. 6 We conclude that ROCK plays a primary role in G-protein-mediated Ca2+ sensitization, which requires MLCK activity, with minor contribution of PKC to the early phase of contraction, and PDBu utilizes conventional PKC(s) in airway smooth muscle.

Relaxation of contracted rabbit tracheal and human bronchial smooth muscle by Y-27632 through inhibition of Ca2+ sensitization

The mechanism of Ca2+ sensitization of contraction has not been elucidated in airway smooth muscle (SM). To determine the role of a small G protein, rhoA p21, and its target protein, rho-associated coiled coil-forming protein kinase (ROCK), in receptor-coupled Ca2+ sensitization of airway SM, we studied the effect of (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexane carboxamide dihydrochloride, monohydrate (Y-27632), a ROCK inhibitor, on isometric contractions in rabbit tracheal and human bronchial SM. Y-27632 completely reversed 1 microM carbachol (CCh)-induced contraction of intact trachea with a concentration producing half-maximum inhibition of effect (IC50) of 1.29 +/- 0.2 microM (n = 5). Although 4beta-phorbol 12,13-dibutyrate (1 microM)-induced Ca2+ sensitization was relatively resistant to Y-27632 in alpha-toxin-permeabilized trachea, CCh (100 microM) plus guanosine triphosphate (GTP) (3 microM)- and guanosine 5'-O-(3'-thiotriphosphate) (10 microM)-induced contractions were relaxed completely by Y-27632 with IC50 of 1.44 +/- 0.3 (n = 6) and 1.15 +/- 0.3 microM (n = 6). Endothelin-1 (1 microM) plus GTP (3 microM)- developed force was also reversed by Y-27632 with IC50 of 4. 10 +/- 1.1 microM (n = 6) in the alpha-toxin-permeabilized bronchus. Both the rabbit and human SM expressed rhoA p21, ROCK I, and its isoform ROCK II. Collectively, rho/ROCK-mediated Ca2+ sensitization plays a central role in the sustained phase of airway SM contraction, and selective inhibition of this pathway may become a new strategy to resolve airflow limitation in asthma.

ET(A) receptors are the primary mediators of myofilament calcium sensitization induced by ET-1 in rat pulmonary artery smooth muscle: a tyrosine kinase independent pathway

We have investigated the possibility that ET-1 can induce an increase in myofilament calcium sensitivity in pulmonary artery smooth muscle. Arterial rings were permeabilized using alpha-toxin (120 microg ml(-1)), in the presence of A23187 (10 microM) to 'knock out' Ca2+ stores, and pre-constricted with pCa 6.8 (buffered with 10 mM EGTA). In the presence of this fixed Ca2+ concentration, 1 microM ET-1 induced a sustained, reversible constriction of 0.15 mN. Pulmonary arterial rings were freeze-clamped at the peak of the induced constriction (time matched). Subsequent densitometric analysis revealed that ET-1 (1 microM) increased the level of phosphorylated myosin light chains by 34% compared to an 11% increase in the presence of pCa 6.8 alone. In contrast to ET-1, the selective ET(B) receptor agonist Sarafotoxin S6C (100 nM) failed to induce a significant constriction. The constriction induced by 1 microM ET-1 was reversibly inhibited when the preparation was preincubated (15 min) with the ETA receptor antagonist BQ 123 (100 microM). The constriction measured 0.13 mN in the absence and 0.07 mN in the presence of 100 microM BQ 123. In contrast, the constriction induced by 1 microM ET-1 measured 0.19 mN in the absence and 0.175 mN following a 15 min pre-incubation with the ET(B) antagonist BQ 788 (100 microM). The constriction induced by 1 microM ET-1 measured 0.14 mN in the presence and 0.13 mN following pre-incubation with the tyrosine kinase inhibitor Tyrphostin A23 (100 microM). We conclude that ET-1 induced an increase in myofilament calcium sensitivity in rat pulmonary arteries via the activation of ET(A) receptors and by a mechanism(s) independent of tyrosine kinase.

Mechanisms of 5-hydroxytryptamine-induced inhibition in the porcine myometrium

The present experiments were designed to clarify the mechanisms of the inhibitory response of 5-hydroxytryptamine (5-HT) in the porcine uterine circular muscle. Inhibitory responses induced by 5-HT (1 nM-1 microM) were not affected by apamin (1 microM), charybdotoxin (100 nM) or glibenclamide (20 microM) but were significantly attenuated by 4-aminopyridine (3 mM) and tetraethylammonium (3 mM). Imidazole (100 microM) decreased but 3-isobutyl-1-methylxanthine (30 microM), milrinone (30 microM) and Ro 20-1724 (10 and 30 microM) potentiated the 5-HT-induced inhibition. On the other hand, zaprinast (3-30 microM) had no significant effect on the inhibitory response of 5-HT. 5-HT caused a time (0-5 min)-and concentration (1 nM-1 microM)-dependent increase in the tissue cyclic AMP level, but had no effect on the tissue cyclic GMP level. A significant correlation (P < 0.05) was observed between the inhibition of contraction and tissue cyclic AMP level. The effect of 5-HT on contractile force and cytosolic Ca2+ level ([Ca2+]i) was investigated using fura-PE3-loaded myometrial strips. A low concentration of 5-HT (< or = 10 nM) inhibited the spontaneous contraction without changing the amplitude of the spontaneous [Ca2+]i increase, but a higher concentration of 5-HT (> or = 100 nM) decreased the resting [Ca2+]i and inhibited both the spontaneous [Ca2+]i increase and spontaneous contraction. High-K+ (50 mM) caused increases in muscle contractile force and [Ca2+]i. 5-HT concentrationdependently inhibited the high-K(+)-induced contraction (EC50, 45 nM) with only a small decrease in [Ca2+]i increase. Carbachol also caused increases in muscle contractile force and [Ca2+]i. 5-HT significantly decreased both the carbachol-induced contraction and [Ca2+]i increase, but was more potent at inhibition of contractile force than [Ca2+]i. In Ca(2+)-loaded myometrial strips, carbachol, but not caffeine, caused a transient increase in [Ca2+]i and contraction in the absence of external Ca2+ (EGTA, 1 mM). 5-HT inhibited both the carbachol-induced increases in [Ca2+]i release and contractile force. In the beta-escin permeabilized myometrium, 5-HT significantly inhibited the Ca(2+)-induced contraction. The present results indicate that 5-HT stimulates tissue cyclic AMP production, and inhibits the porcine uterine muscle contractility by a reduction in [Ca2+]i and in Ca2+ sensitivity of the contractile elements. Activation of K+ channels might be partially involved in 5-HT-induced inhibition of the myometrial contractility.

InsP3, but not novel Ca2+ releasers, contributes to agonist-initiated contraction in rabbit airway smooth muscle

1. To examine the contributions of the putative Ca2+ releasers, inositol 1,4,5-trisphosphate (InsP3), cyclic ADP ribose (cADPR), and nicotinate adenine dinucleotide phosphate (NAADP), to carbachol (CCh)-induced contraction in airway smooth muscle, we measured force development of permeabilized rabbit tracheal smooth muscle, human bronchial smooth muscle and guinea-pig ileum longitudinal smooth muscle. 2. In the presence of 50 microM GTP, CCh and InsP3 contracted alpha-toxin-permeabilized tracheal smooth muscle dose dependently; the EC50 values for CCh and InsP3 were 1.84 microM and 363 microM, and the maximum responses (normalized to the 30 mM caffeine response) to 100 microM CCh and to 800 microM InsP3 were 206 +/- 13.4 % (mean +/- S.E.M.) and 84.4 +/- 5.3 %, respectively. 3. However, cADPR (10-300 microM), beta-NAD+ (2.5 mM), FK506 (30 microM) and NAADP (100 microM) neither contracted the strip by themselves nor affected the subsequent CCh (1 microM) response. alpha-Toxin-permeabilized bronchial smooth muscle and ileum smooth muscle also responded to caffeine, InsP3 and CCh but not to cADPR. 4. Both 100 microM 8-amino-cADPR, a selective cADPR antagonist, and 100 microM thionicotinamide-NADP, a selective NAADP antagonist, failed to inhibit the CCh response, although procaine abolished the caffeine, InsP3 and CCh responses in the permeabilized tracheal smooth muscle. 5. Although inhibition of the caffeine response by 30 microM ryanodine was nearly complete, approximately 30 % of the InsP3 (300 microM) plus GTP (50 microM) response was retained, and the resultant response disappeared after the caffeine response was evoked in the presence of ryanodine. 6. Heparin (300 microg ml-1) blocked InsP3 (300 microM) and CCh (3 microM) responses in beta-escin-permeabilized tracheal smooth muscle, while Ruthenium Red (100 microM) partially inhibited the CCh response. 7. Collectively, InsP3 but not cADPR or NAADP plays a key role in CCh-initiated contraction, and InsP3 utilizes a single compartment of the caffeine/ryanodine-sensitive stored Ca2+ in airway smooth muscle.

Receptor-dependent G protein-mediated Ca2+ sensitization in canine airway smooth muscle

To determine the mechanisms of receptor-dependent Ca2+ sensitization in airway smooth muscle, canine tracheal smooth muscle (CTSM) was permeabilized with alpha-toxin or beta-escin. Although the effects of 5-hydroxytryptamine (100 microM), histamine (100 microM), and the thromboxane A2 analogue U-46619 (100 microM) were negligible, carbachol (100 microM) and endothelin-1 (ET-1, 1 microM) evoked additional contractions of 47.0 +/- 5.90% and 25.0 +/- 5.37% (n = 6) at pCa 6.7 with GTP (3 microM) (normalized to the maximum contraction at pCa 4.5) in alpha-toxin-permeabilized CTSM. GDP-beta-S (1 mM) reversed the carbachol and ET-1 responses completely. GTP-gamma-S (30 microM) and 4 beta-phorbol 12,13-dibutyrate (PDBu, 3 microM) increased the Ca2+ sensitivity (median effective pCa) of contraction by 1.8- and 4.4-fold, respectively (n = 4-11, P < 0.05). The effects of saturating concentrations of GTP-gamma-S and PDBu were additive. A synthetic peptide (T2) corresponding to the actin-binding site of calponin caused a dose-dependent contraction of beta-escin permeabilized CTSM, with the peak effect (25 +/- 4%, n = 4) at 1200 microM, PDBu (3 microM) caused contraction of the T2 peptide-treated CTSM. In conclusion, Ca2+ sensitization of CTSM depends on receptor type and is mediated by G proteins and protein kinase C whose effects are additive, with a partial contribution by calponin.

Rho-associated kinase directly induces smooth muscle contraction through myosin light chain phosphorylation

Small GTPase Rho plays pivotal roles in the Ca2+ sensitization of smooth muscle. However, the GTP-bound active form of Rho failed to exert Ca2+-sensitizing effects in extensively Triton X-100-permeabilized smooth muscle preparations, due to the loss of the important diffusible cofactor (Gong, M. C., Iizuka, K., Nixon, G. , Browne, J. P., Hall, A., Eccleston, J. F., Sugai, M., Kobayashi, S. , Somlyo, A. V., and Somlyo, A. P. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 1340-1345). Here we demonstrate the contractile effects of Rho-associated kinase (Rho-kinase), recently identified as a putative target of Rho, on the Triton X-100-permeabilized smooth muscle of rabbit portal vein. Introduction of the constitutively active form of Rho-kinase into the cytosol of Triton X-100-permeabilized smooth muscle provoked a contraction and a proportional increase in levels of monophosphorylation of myosin light chain in both the presence and the absence of cytosolic Ca2+. These effects of constitutively active Rho-kinase were wortmannin (a potent myosin light chain kinase inhibitor)-insensitive. Immunoblot analysis revealed that the amount of native Rho-kinase was markedly lower in Triton X-100-permeabilized tissue than in intact tissue. Our results demonstrate that Rho-kinase directly modulates smooth muscle contraction through myosin light chain phosphorylation, independently of the Ca2+-calmodulin-dependent myosin light chain kinase pathway.

Regions of the 110-kDa regulatory subunit M110 required for regulation of myosin-light-chain-phosphatase activity in smooth muscle

To characterize the in situ interactions between the subunits (regulatory 110 kDa, M110; 21-kDa, M21 and catalytic, 37-kDa, PP1c) of smooth muscle myosin phosphatase (SMPP-1M), we determined, in Triton-X-100-permeabilized rabbit portal vein contracted with microcystin-LR, the ability of the following fragments of M110 to regulate relaxation induced by exogenous PP1c: (a) M110 purified from pig bladder; (b) the 72.5-kDa N-terminal fragment expressed from rat kidney cDNA [glutathione-S-transferase-M110-(11-612)-peptide]; (c) a 58-kDa fragment, the N-terminal degradation product of M110 (M58); (d) two fragments expressed from rat aorta cDNA [M110-(1-309)-peptide and M110-(39-309)-peptide]; a synthetic fragment of M110 [M110-(1-38)-peptide]. The M110/M21 complex accelerated approximately 1.6-fold the rate of dephosphorylation of the myosin P-light chain and also relaxation induced by PP1c. The glutathione-S-transferase-M110-(11-612)-peptide and the M58 fragments, as well as the M110-(1-309)-peptide and, at higher concentration, M110-(1-38)-peptide, had similar effects that did not require the M21 subunit. Arachidonic acid, known to dissociate PP1c from the native holoenzyme and inhibit SMPP-1M activity, inhibited the regulatory action of the M110/M21 complex on PP1c activity and, to a lesser extent that of the glutathione-S-transferase-M110-(11-612)-peptide, but not that of the M58 fragment or of the shorter peptides. We conclude that, consistent with in vitro studies [8], the N-terminal sequence (1-309) of the M110 subunit is also sufficient to enhance the activity of PP1c for myosin in muscle. However, its C-terminal half (downstream from the M58 fragment) is required for inhibition by arachidonic acid. In contrast to the effect of the M110 subunit and its fragments, a peptide, corresponding to part of the PP1c-binding site of the regulatory glycogen-binding subunit from skeletal muscle GM [GM-(63-93)-peptide], specifically slowed the relaxation, induced by flash photolysis of diazo-2, of Triton X-100-permeabilized femoral artery strips, and inhibited the holoenzyme-induced relaxation in the portal vein, suggesting that the GM subunit can compete with the regulatory effect of M110 on PP1c in smooth muscle.

Kinetics of prephosphorylation reactions and myosin light chain phosphorylation in smooth muscle. Flash photolysis studies with caged calcium and caged ATP

The pre-myosin light chain (MLC20) phosphorylation components of the lag phase (td) of contractile activation were determined in permeabilized smooth muscles activated by photolytic release of ATP from caged ATP and/or Ca2+ from 4-(2-nitrophenyl)-EGTA (NP-EGTA). Calmodulin (CaM) shortened the td (470 ms at 0 added CaM) that followed Ca2+ release, but its effect (td = approximately 200 ms) saturated at 40 microM. Photolysis of caged ATP following preequilibration with identical [Ca4CaM] shortened td to 41 ms. The rate of phosphorylation was very fast (3.5 s-1 at 22 degrees C in the presence of 5 microM exogenous CaM) following photolysis of caged ATP, and, following Ca2+ release, phosphorylation was accelerated by CaM. Simultaneous photolysis of caged ATP and NP-EGTA was followed by a td of 194 ms at 5 microM CaM and a rate of MLC20 phosphorylation intermediate between these parameters following photolysis of, respectively, NP-EGTA and caged ATP. In the presence of the normal, total endogenous CaM content (37 +/- 4 microM) of protal vein smooth muscles td was 565 ms. Steady state maximum force at pCa 5.5 was increased by much lower (100 nM) exogenous [CaM] than was required (> 2.5 microM) to shorten the td. We estimate the endogenous CaM available under steady state conditions in vivo to be approximately 0.25 microM and probably less during a rapid Ca2+ transient. We conclude that the [CaM] dependence of the kinetics of MLC20 phosphorylation and force development (t1/2 and td) initiated by Ca2+ reflects the recruitment of a slowly diffusible component of total CaM. The relatively long duration of td (197 ms) at saturating [CaM] suggests the contribution to td of an additional component, possibly a prephosphorylation activation/isomerization of the Ca4CaM myosin light chain kinase complex (Török, K., and Trentham, D. R. (1994) Biochemistry 33, 12807-12820). The relatively short delay (108 ms in the presence of 40 microM CaM) following simultaneous photolysis of NP-EGTA and caged ATP suggests that preincubation with ATP (prior to photolysis of NP-EGTA) may inhibit the formation of a preactive Ca2CaM myosin light chain kinase complex.

Phosphorylation of caldesmon by mitogen-activated protein kinase with no effect on Ca2+ sensitivity in rabbit smooth muscle

1. Recombinant, activated mitogen-activated protein kinase (3.3 microM; p42mapk) phosphorylated caldesmon in phasic (rabbit portal vein) and tonic (rabbit femoral artery) smooth muscle strips permeabilized with Triton X-100. 2. Phosphorylation of caldesmon by p42mapk neither induced contraction of relaxed smooth muscle nor affected the Ca2+ sensitivity of submaximally contracted permeabilized phasic or tonic smooth muscle.

Reversible permeabilization. A novel technique for the intracellular introduction of antisense oligodeoxynucleotides into intact smooth muscle

Antisense oligodeoxynucleotides (ODNs) have been used to modify gene expression in vitro and are also promising therapeutic agents. Although there are numerous reports of antisense ODN-mediated changes in protein expression of cultured cells, use of these compounds to achieve antisense regulation of specific proteins in intact tissue has been limited. The aims of this study were (1) to define organ culture conditions for ileum smooth muscle that would permit long-term maintenance of force-generating capabilities and normal ultrastructure and (2) to develop a method for efficient introduction of antisense ODNs into intact tissue. Sheets of ODN-containing, reversibly permeabilized rat outer longitudinal ileum were maintained in a serum-free organ culture medium for 1 week without significant decreases in tension response to membrane depolarization or carbachol stimulation; the G protein-coupled calcium sensitization pathway was also intact after 7 days. Reversible permeabilization, a method previously used to load smooth and cardiac muscle with aequorin and heparin, was effective for loading > 95% of ileum smooth muscle cells with a fluorescein-conjugated antisense ODN (5'-AAGGGCCATTTTGTT-FITC-3'). Confocal microscopy of reversibly permeabilized smooth muscle loaded with fluorescent antisense ODNs revealed intense nuclear fluorescence and less intense, homogeneous, cytoplasmic fluorescence. Internally radiolabeled ODNs (homologous to the above sequence) showed complete degradation between 4 and 16 hours after introduction into the cells. In summary, we have demonstrated methods for long-term organ culture and high-efficiency introduction of antisense ODNs into intact smooth muscle sheets. Such methods have broad potential utility for investigating many questions in smooth muscle biology. At present, however, a major limitation of this approach is the short half-life of phosphorothioated ODNs.