Expression of olfactory-type cyclic nucleotide-gated channel (CNGA2) in vascular tissues

Wall Shear Stress Reduction Activates Angiotensin II to Facilitate Aneurysmal Subarachnoid Hemorrhage in Intracranial Aneurysms Through MicroRNA-29/The Growth Factor-Beta Receptor Type II/Smad3 Axis

OBJECTIVE

We tried to broaden our knowledge of the possible role of wall shear stress (WSS) in the occurrence of intracranial aneurysms (IAs).

METHODS

Genes implicated in IAs and genes related to WSS were predicted through in silico analysis. Rat models of IAs were established, in which the expression patterns of angiotensin II (Ang II) were characterized, and WSS was assessed. Vascular endothelial cells isolated from rats bearing IAs were treated with microRNA-29 (miR-29) mimic/inhibitor, small interfering RNA-TGF-β receptor type II (TGFBR2)/overexpressed TGFBR2, Ang II, or angiotensin-converting enzyme (ACE) inhibitor. Then, the endothelial-to-mesenchymal transition (EndMT) was evaluated by flow cytometry. Finally, the volume of IAs and risk of subarachnoid hemorrhage were analyzed in vivo in response to miR-29 gain of function.

RESULTS

WSS was decreased in the IA bearing arteries, which showed a positive correlation with ACE and Ang II in the vascular tissues of IA rats. Reduced miR-29 and increased ACE, Ang II, and TGFBR2 were detected in the vascular tissues of IA rats. Ang II inhibited miR-29, which targeted TGFBR2. Downregulated TGFBR2 was accompanied by suppression of Smad3 phosphorylation. Through impairing miR-29-dependent inhibition of TGFBR2, Ang II enhanced EndMT. In vivo data confirmed that treatment of miR-29 agomir delayed the formation of IA and decreased the risk of subarachnoid hemorrhage.

CONCLUSIONS

The current study provided evidence that WSS reduction could activate Ang II, reduce miR-29 expression, and activate the TGFBR2/Smad3 axis, thus promoting EndMT and accelerating the progression of IAs.

PDE-Mediated Cyclic Nucleotide Compartmentation in Vascular Smooth Muscle Cells: From Basic to a Clinical Perspective

Cardiovascular diseases are important causes of mortality and morbidity worldwide. Vascular smooth muscle cells (SMCs) are major components of blood vessels and are involved in physiologic and pathophysiologic conditions. In healthy vessels, vascular SMCs contribute to vasotone and regulate blood flow by cyclic nucleotide intracellular pathways. However, vascular SMCs lose their contractile phenotype under pathological conditions and alter contractility or signalling mechanisms, including cyclic nucleotide compartmentation. In the present review, we focus on compartmentalized signaling of cyclic nucleotides in vascular smooth muscle. A deeper understanding of these mechanisms clarifies the most relevant axes for the regulation of vascular tone. Furthermore, this allows the detection of possible changes associated with pathological processes, which may be of help for the discovery of novel drugs.

Ending Restenosis: Inhibition of Vascular Smooth Muscle Cell Proliferation by cAMP

Increased vascular smooth muscle cell (VSMC) proliferation contributes towards restenosis after angioplasty, vein graft intimal thickening and atherogenesis. The second messenger 3′ 5′ cyclic adenosine monophosphate (cAMP) plays an important role in maintaining VSMC quiescence in healthy vessels and repressing VSMC proliferation during resolution of vascular injury. Although the anti-mitogenic properties of cAMP in VSMC have been recognised for many years, it is only recently that we gained a detailed understanding of the underlying signalling mechanisms. Stimuli that elevate cAMP in VSMC inhibit G₁-S phase cell cycle progression by inhibiting expression of cyclins and preventing S-Phase Kinase Associated Protein-2 (Skp2-mediated degradation of cyclin-dependent kinase inhibitors. Early studies implicated inhibition of MAPK signalling, although this does not fully explain the anti-mitogenic effects of cAMP. The cAMP effectors, Protein Kinase A (PKA) and Exchange Protein Activated by cAMP (EPAC) act together to inhibit VSMC proliferation by inducing Cyclic-AMP Response Element Binding protein (CREB) activity and inhibiting members of the RhoGTPases, which results in remodelling of the actin cytoskeleton. Cyclic-AMP induced actin remodelling controls proliferation by modulating the activity of Serum Response Factor (SRF) and TEA Domain Transcription Factors (TEAD), which regulate expression of genes required for proliferation. Here we review recent research characterising these mechanisms, highlighting novel drug targets that may allow the anti-mitogenic properties of cAMP to be harnessed therapeutically to limit restenosis.

Adenosine receptors regulate gap junction coupling of the human cerebral microvascular endothelial cells hCMEC/D3 by Ca2+ influx through cyclic nucleotide-gated channels

KEY POINTS

Gap junction channels are essential for the formation and regulation of physiological units in tissues by allowing the lateral cell-to-cell diffusion of ions, metabolites and second messengers. Stimulation of the adenosine receptor subtype A_2B increases the gap junction coupling in the human blood-brain barrier endothelial cell line hCMEC/D3. Although the increased gap junction coupling is cAMP-dependent, neither the protein kinase A nor the exchange protein directly activated by cAMP were involved in this increase. We found that cAMP activates cyclic nucleotide-gated (CNG) channels and thereby induces a Ca²⁺ influx, which leads to the increase in gap junction coupling. The report identifies CNG channels as a possible physiological link between adenosine receptors and the regulation of gap junction channels in endothelial cells of the blood-brain barrier.

ABSTRACT

The human cerebral microvascular endothelial cell line hCMEC/D3 was used to characterize the physiological link between adenosine receptors and the gap junction coupling in endothelial cells of the blood-brain barrier. Expressed adenosine receptor subtypes and connexin (Cx) isoforms were identified by RT-PCR. Scrape loading/dye transfer was used to evaluate the impact of the A_2A and A_2B adenosine receptor subtype agonist 2-phenylaminoadenosine (2-PAA) on the gap junction coupling. We found that 2-PAA stimulated cAMP synthesis and enhanced gap junction coupling in a concentration-dependent manner. This enhancement was accompanied by an increase in gap junction plaques formed by Cx43. Inhibition of protein kinase A did not affect the 2-PAA-related enhancement of gap junction coupling. In contrast, the cyclic nucleotide-gated (CNG) channel inhibitor l-cis-diltiazem, as well as the chelation of intracellular Ca²⁺ with BAPTA, or the absence of external Ca²⁺ , suppressed the 2-PAA-related enhancement of gap junction coupling. Moreover, we observed a 2-PAA-dependent activation of CNG channels by a combination of electrophysiology and pharmacology. In conclusion, the stimulation of adenosine receptors in hCMEC/D3 cells induces a Ca²⁺ influx by opening CNG channels in a cAMP-dependent manner. Ca²⁺ in turn induces the formation of new gap junction plaques and a consecutive sustained enhancement of gap junction coupling. The report identifies CNG channels as a physiological link that integrates gap junction coupling into the adenosine receptor-dependent signalling of endothelial cells of the blood-brain barrier.

'Smelling' the cerebrospinal fluid: olfactory signaling molecules are expressed in and mediate chemosensory signaling from the choroid plexus

The olfactory-type signaling machinery has been known to be involved not only in odorant detection but also in other tissues with unsuspected sensory roles. As a barrier, the choroid plexus (CP) is an active participant in the monitoring of the cerebrospinal fluid (CSF), promptly responding to alterations in its composition. We hypothesized that olfactory signaling could be active in CP, contributing to the surveillance of the CSF composition. We determined the mRNA and protein expression of the major components of the olfactory transduction pathway in the rat CP, including odorant receptors, the olfactory G-protein (Gαolf), adenylate cyclase 3 and cyclic nucleotide-gated channel 2. The functionality of the transduction pathway and the intracellular mechanisms involved were analyzed by DC field potential recording electrophysiological analysis, in an ex vivo CP-brain setup, using polyamines as stimuli and blockers of the downstream signaling pathways. Concentration-dependent responses were obtained for the polyamines studied (cadaverine, putrescine, spermine and spermidine), all known to be present in the CSF. Transfection of a CP epithelial cell line with siRNA against Gαolf effectively knocked down protein expression and reduced the CP cells' response to spermine. Thus, the key components of the olfactory chemosensory apparatus are present and are functional in murine CP, and polyamines seem to trigger both the cAMP and the phospholipase C-inositol 1,4,5-trisphosphate pathways. Olfactory-like chemosensory signaling may be an essential component of the CP chemical surveillance apparatus to detect alterations in the CSF composition, and to elicit responses to modulate and maintain brain homeostasis.

The first mutation in CNGA2 in two brothers with anosmia

Isolated congenital anosmia (ICA) is a rare disorder, where otherwise healthy individuals present with an inability to smell since birth. A list of studies have described the genes involved in syndromic anosmia; however, the genetics of ICA is still in its infancy. Studies in mice show that the cyclic nucleotide-gated channel subunit CNGA2, expressed in the olfactory epithelium has a crucial role in olfactory signal transduction. We have identified a novel X-linked stop mutation in CNGA2 (c.634C>T, p.R212*) in two brothers with ICA using exome sequencing. No additional mutations in CNGA2 were identified in a cohort of 31 non-related ICA individuals. Magnetic resonance brain imaging revealed diminished olfactory bulbs and flattened olfactory sulci. This is the first report of a mutation in the cyclic nucleotide-gated gene CNGA2 and supports the critical role of this gene in human olfaction.

Comprehensive RNA-Seq expression analysis of sensory ganglia with a focus on ion channels and GPCRs in Trigeminal ganglia

The specific functions of sensory systems depend on the tissue-specific expression of genes that code for molecular sensor proteins that are necessary for stimulus detection and membrane signaling. Using the Next Generation Sequencing technique (RNA-Seq), we analyzed the complete transcriptome of the trigeminal ganglia (TG) and dorsal root ganglia (DRG) of adult mice. Focusing on genes with an expression level higher than 1 FPKM (fragments per kilobase of transcript per million mapped reads), we detected the expression of 12984 genes in the TG and 13195 in the DRG. To analyze the specific gene expression patterns of the peripheral neuronal tissues, we compared their gene expression profiles with that of the liver, brain, olfactory epithelium, and skeletal muscle. The transcriptome data of the TG and DRG were scanned for virtually all known G-protein-coupled receptors (GPCRs) as well as for ion channels. The expression profile was ranked with regard to the level and specificity for the TG. In total, we detected 106 non-olfactory GPCRs and 33 ion channels that had not been previously described as expressed in the TG. To validate the RNA-Seq data, in situ hybridization experiments were performed for several of the newly detected transcripts. To identify differences in expression profiles between the sensory ganglia, the RNA-Seq data of the TG and DRG were compared. Among the differentially expressed genes (> 1 FPKM), 65 and 117 were expressed at least 10-fold higher in the TG and DRG, respectively. Our transcriptome analysis allows a comprehensive overview of all ion channels and G protein-coupled receptors that are expressed in trigeminal ganglia and provides additional approaches for the investigation of trigeminal sensing as well as for the physiological and pathophysiological mechanisms of pain.

Update on vascular endothelial Ca2+ signalling: A tale of ion channels, pumps and transporters

A monolayer of endothelial cells (ECs) lines the lumen of blood vessels and forms a multifunctional transducing organ that mediates a plethora of cardiovascular processes. The activation of ECs from as state of quiescence is, therefore, regarded among the early events leading to the onset and progression of potentially lethal diseases, such as hypertension, myocardial infarction, brain stroke, and tumor. Intracellular Ca²⁺ signals have long been know to play a central role in the complex network of signaling pathways regulating the endothelial functions. Notably, recent work has outlined how any change in the pattern of expression of endothelial channels, transporters and pumps involved in the modulation of intracellular Ca²⁺ levels may dramatically affect whole body homeostasis. Vascular ECs may react to both mechanical and chemical stimuli by generating a variety of intracellular Ca²⁺ signals, ranging from brief, localized Ca²⁺ pulses to prolonged Ca²⁺ oscillations engulfing the whole cytoplasm. The well-defined spatiotemporal profile of the subcellular Ca²⁺ signals elicited in ECs by specific extracellular inputs depends on the interaction between Ca²⁺ releasing channels, which are located both on the plasma membrane and in a number of intracellular organelles, and Ca²⁺ removing systems. The present article aims to summarize both the past and recent literature in the field to provide a clear-cut picture of our current knowledge on the molecular nature and the role played by the components of the Ca²⁺ machinery in vascular ECs under both physiological and pathological conditions.

Heterogeneity in relaxation of different sized porcine coronary arteries to nitrovasodilators: role of PKG and MYPT1

The present study was to determine the role of the type I isoform of cGMP-dependent protein kinase (PKG I) and its downstream effector myosin phosphatase target subunit 1 (MYPT1) in the responses of different sized coronary arteries to nitrovasodilators. Relaxations of isolated porcine coronary arteries were determined by isometric tension recording technique. Protein levels of PKG I and its effectors were analyzed by Western blotting. The activities of PKG I and MYPT1 were studied by analyzing phosphorylation of vasodilator-stimulated phosphoprotein (VASP) and MYPT1, respectively. Nitroglycerin, DETA NONOate, and 8-Br-cGMP caused greater relaxations in large than in small coronary arteries. Relaxations were attenuated to a greater extent by Rp-8-Br-PET-cGMPS (a PKG inhibitor) in large vs. small arteries. The expressions of PKG I and MYPT1 in large arteries were more abundant than in small arteries. DETA NONOate stimulated phosphorylation of VASP at Ser239 and inhibited phosphorylation of MYPT1 at Thr853 to a greater extent in large than in small arteries. A suppressed phosphorylation of MYPT1 at Thr853 was caused by 8-Br-cGMP in large but not small arteries, which was inhibited by Rp-8-Br-PET-cGMPS. These results suggest that the greater responsiveness of large coronary arteries to nitrovasodilators result in part from greater activities of PKG I and MYPT1. Dysfunction in nitric oxide signaling is implicated in the vulnerability of large coronary arteries to certain disorders such as atherosclerosis and spasm. Augmentation of PKG I-MYPT1 signaling may be of therapeutic benefit for combating these events.

PDE1 isozymes, key regulators of pathological vascular remodeling

Pathological vascular remodeling is a hallmark of most vascular disorders such as atherosclerosis, postangioplasty restenosis, allograft vasculopathy, and pulmonary hypertension. Pathological vascular remodeling is a multi-cell-dependent process leading to detrimental changes of vessel structure and eventual vessel occlusion. Cyclic nucleotide signaling regulates a variety of vascular functions ranging from cell contractility to cell growth. Cyclic nucleotide phosphodiesterases (PDEs), a large family of structurally and functionally distinct isozymes, regulate cyclic nucleotide levels and compartmentalization through catalyzing their degradation reaction. Increasing evidence has suggested that one of the important mechanisms for specific cyclic nucleotide regulation is exerted through selective activation or inhibition of distinct PDE isozymes. This review summarizes the work done to characterize the role and therapeutic potential of PDE1 isozymes in pathological vascular remodeling.

Cyclic nucleotide phosphodiesterase 1 regulates lysosome-dependent type I collagen protein degradation in vascular smooth muscle cells

OBJECTIVE

The phenotypic modulation of vascular smooth muscle cells (VSMCs) to a synthetic phenotype is vital during pathological vascular remodeling and the development of various vascular diseases. An increase in type I collagen (collagen I) has been implicated in synthetic VSMCs, and cyclic nucleotide signaling is critical in collagen I regulation. Herein, we investigate the role and underlying mechanism of cyclic nucleotide phosphodiesterase 1 (PDE1) in regulating collagen I in synthetic VSMCs.

METHODS AND RESULTS

The PDE1 inhibitor IC86340 significantly reduced collagen I in human saphenous vein explants undergoing spontaneous remodeling via ex vivo culture. In synthetic VSMCs, high basal levels of intracellular and extracellular collagen I protein were markedly decreased by IC86340. This attenuation was due to diminished protein but not mRNA. Inhibition of lysosome function abolished the effect of IC86340 on collagen I protein expression. PDE1C but not PDE1A is the major isoform responsible for mediating the effects of IC86340. Bicarbonate-sensitive soluble adenylyl cyclase/cAMP signaling was modulated by PDE1C, which is critical in collagen I degradation in VSMCs.

CONCLUSIONS

These data demonstrate that PDE1C regulates soluble adenylyl cyclase/cAMP signaling and lysosome-mediated collagen I protein degradation, and they suggest that PDE1C plays a critical role in regulating collagen homeostasis during pathological vascular remodeling.

Cyclic nucleotide-gated channels contribute to thromboxane A2-induced contraction of rat small mesenteric arteries

Background

Thromboxane A₂ (TxA₂)-induced smooth muscle contraction has been implicated in cardiovascular, renal and respiratory diseases. This contraction can be partly attributed to TxA₂-induced Ca²⁺ influx, which resulted in vascular contraction via Ca²⁺-calmodulin-MLCK pathway. This study aims to identify the channels that mediate TxA₂-induced Ca²⁺ influx in vascular smooth muscle cells.

Methodology/Principal Findings

Application of U-46619, a thromboxane A₂ mimic, resulted in a constriction in endothelium-denuded small mesenteric artery segments. The constriction relies on the presence of extracellular Ca²⁺, because removal of extracellular Ca²⁺ abolished the constriction. This constriction was partially inhibited by an L-type Ca²⁺ channel inhibitor nifedipine (0.5–1 µM). The remaining component was inhibited by L-cis-diltiazem, a selective inhibitor for CNG channels, in a dose-dependent manner. Another CNG channel blocker LY83583 [6-(phenylamino)-5,8-quinolinedione] had similar effect. In the primary cultured smooth muscle cells derived from rat aorta, application of U46619 (100 nM) induced a rise in cytosolic Ca²⁺ ([Ca²⁺]_i), which was inhibited by L-cis-diltiazem. Immunoblot experiments confirmed the presence of CNGA2 protein in vascular smooth muscle cells.

Conclusions/Significance

These data suggest a functional role of CNG channels in U-46619-induced Ca²⁺ influx and contraction of smooth muscle cells.

Cyclic nucleotide-gated channels: a familiar channel family with a new function?

The cyclic nucleotide-gated (CNG) channel is a family of nonselective cation channels that open in response to an elevated cyclic nucleotide level. Cyclic nucleotides, particularly cAMP and cGMP, govern a great diversity of cellular functions. While the pivotal roles of CNG channels in the visual and olfactory systems have been well established in the past decade, relatively few studies were performed regarding the functional roles of CNG channels in non-neuronal systems. Cyclic nucleotides and Ca2+ are key signaling molecules in cardiovascular systems. Given that CNG channels are expressed in vascular tissues, several recent studies have explored the possible functional role of CNG channels in cardiovascular systems. This article intends to summarize some recent developments regarding the expression and functional role of CNG channels in the cardiovascular system.

Store-operated calcium entry channels in pulmonary endothelium: the emerging story of TRPCS and Orai1

Cells of diverse origin utilize shifts in cytosolic calcium concentrations as intracellular signals to elicit physiological responses. In endothelium, inflammatory first messengers increase cytosolic calcium as a signal to disrupt cell-cell borders and produce inter-cellular gaps. Calcium influx across the plasma membrane is required to initiate barrier disruption, although the calcium entry mechanism responsible for this effect remains poorly understood. This chapter highlights recent efforts to define the molecular anatomy of the ion channel responsible for triggering endothelial cell gap formation. Resolving the identity and function of this calcium channel will pave the way for new anti-inflammatory therapeutic targets.

Role of cyclic nucleotides in the control of cytosolic Ca2+ levels in vascular endothelial cells

1. Endothelial cells have a key role in the cardiovascular system. Most endothelial cell functions depend on changes in cytosolic Ca(2+) concentrations ([Ca(2+)](i)) to some extent and Ca2+ signalling acts to link external stimuli with the synthesis and release of regulatory factors in endothelial cells. The [Ca(2+)](i) is maintained by a well-balanced Ca(2+) flux across the endoplasmic reticulum and plasma membrane. 2. Cyclic nucleotides, such as cAMP and cGMP, are very important second messengers. The cyclic nucleotides can affect [Ca(2+)](i) directly or indirectly (via the actions of protein kinase (PK) A or PKG-mediated phosphorylation) by regulating Ca(2+) mobilization and Ca(2+) influx. Fine-tuning of [Ca(2+)](i) is also fundamental to protect endothelial cells against damaged caused by the excessive accumulation of Ca(2+). 3. Therapeutic agents that control cAMP and cGMP levels have been used to treat various cardiovascular diseases. 4. The aim of the present review is to discuss: (i) the functions of endothelial cells; (ii) the importance of [Ca(2+)](i) in endothelial cells; (iii) the impact of excessive [Ca(2+)](i) in endothelial cells; and (iv) the balanced control of [Ca(2+)](i) in endothelial cells via involvement of cyclic nucleotides (cAMP and cGMP) and their general effectors.

Epinephrine-induced Ca2+ influx in vascular endothelial cells is mediated by CNGA2 channels

Epinephrine, through its action on beta-adrenoceptors, may induce endothelium-dependent vascular dilation, and this action is partly mediated by a cytosolic Ca(2+) ([Ca(2+)](i)) change in endothelial cells. In the present study, we explored the molecular identity of the channels that mediate epinephrine-induced endothelial Ca(2+) influx and subsequent vascular relaxation. Patch clamp recorded an epinephrine- and cAMP-activated cation current in the primary cultured bovine aortic endothelial cells (BAECs) and H5V endothelial cells. L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated channels, diminished this cation current. Furthermore, this cation current was greatly reduced by a CNGA2-specific siRNA in H5V cells. With the use of fluorescent Ca(2+) dye, it was found that epinephrine and isoprenaline, a beta-adrenoceptor agonist, induced endothelial Ca(2+) influx in the presence of bradykinin. This Ca(2+) influx was inhibited by L-cis-diltiazem and LY-83583, and by a beta(2)-adrenoceptor antagonist ICI-118551. CNGA2-specific siRNA also diminished this Ca(2+) influx in H5V cells. Furthermore, L-cis-diltiazem and LY-83583 inhibited the endothelial Ca(2+) influx in isolated mouse aortic strips. L-cis-diltiazem also markedly reduced the endothelium-dependent vascular dilation to isoprenaline in isolated mouse aortic segments. In summary, CNG channels, CNGA2 in particular, mediate beta-adrenoceptor agonist-induced endothelial Ca(2+) influx and subsequent vascular dilation.

Are pheromones detected through the main olfactory epithelium?

A major sensory organ for the detection of pheromones by animals is the vomeronasal organ (VNO). Although pheromones control the behaviors of various species, the effect of pheromones on human behavior has been controversial because the VNO is not functional in adults. However, recent genetic, biochemical, and electrophysiological data suggest that some pheromone-based behaviors, including male sexual behavior in mice, are mediated through the main olfactory epithelium (MOE) and are coupled to the type 3 adenylyl cyclase (AC3) and a cyclic nucleotide-gated (CNG) ion channel. These recent discoveries suggest the provocative hypothesis that human pheromones may signal through the MOE.

CNGA2 channels mediate adenosine-induced Ca2+ influx in vascular endothelial cells

OBJECTIVE

Adenosine is a cAMP-elevating vasodilator that induces both endothelium-dependent and -independent vasorelaxation. An increase in cytosolic Ca(2+) ([Ca(2+)](i)) is a crucial early signal in the endothelium-dependent relaxation elicited by adenosine. This study explored the molecular identity of channels that mediate adenosine-induced Ca(2+) influx in vascular endothelial cells.

METHODS AND RESULTS

Adenosine-induced Ca(2+) influx was markedly reduced by L-cis-diltiazem and LY-83583, two selective inhibitors for cyclic nucleotide-gated (CNG) channels, in H5V endothelial cells and primary cultured bovine aortic endothelial cells (BAECs). The Ca(2+) influx was also inhibited by 2 adenylyl cyclase inhibitors MDL-12330A and SQ-22536, and by 2 A(2B) receptor inhibitors MRS-1754 and 8-SPT, but not by an A(2A) receptor inhibitor SCH-58261 or a guanylyl cyclase inhibitor ODQ. Patch clamp experiments recorded an adenosine-induced current that could be inhibited by L-cis-diltiazem and LY-83583. A CNGA2-specific siRNA markedly decreased the Ca(2+) influx and the cation current in H5V cells. Furthermore, L-cis-diltiazem inhibited the endothelial Ca(2+) influx in mouse aortic strips, and it also reduced 5-N-ethylcarboxamidoadenosine (NECA, an A(2) adenosine receptor agonist)-induced vasorelaxation.

CONCLUSIONS

CNGA2 channels play a key role in adenosine-induced endothelial Ca(2+) influx and vasorelaxation. It is likely that adenosine acts through A(2B) receptors and adenylyl cyclases to stimulate CNGA2.

Origin of functional diversity among tetrameric voltage-gated channels

The aim of the present work is to relate functional differences of voltage-gated K(+) (K(v)), hyperpolarization-activated cyclic nucleotide-gated (HCN), and cyclic nucleotide gated (CNG) channels to differences in their amino acid sequences. By means of combined bioinformatic sequence analyses and homology modelling, we suggest that: (1) CNG channels are less voltage-dependent than K(v) channels since the charge of their voltage sensor, the S4 helix, is lower than that of K(v) channels and because of the presence of a conserved proline in the S4-S5 linker, which is quite likely to uncouple S4 from S5 and S6. (2) In HCN channels, S4 features a higher net positive charge with respect to K(v) channels and an extensive network of hydrophobic residues, which is quite likely to provide a tight coupling among S4 and the neighboring helices. We suggest insights on the gating of HCN channels and the reasons why they open with membrane hyperpolarization and with a significantly longer time constant with respect to other channels.

Pheromone detection in male mice depends on signaling through the type 3 adenylyl cyclase in the main olfactory epithelium

Terrestrial vertebrates have evolved two anatomically and mechanistically distinct chemosensory structures: the main olfactory epithelium (MOE) and the vomeronasal organ (VNO). Although it has been generally thought that pheromones are detected through the VNO, whereas other chemicals are sensed by the MOE, recent evidence suggests that some pheromones may be detected through the MOE. Odorant receptors in the MOE are coupled to the type 3 adenylyl cyclase (AC3), an enzyme not expressed in the VNO. Consequently, odorants and pheromones do not elicit electrophysiological responses in the MOE of AC3-/- mice, although VNO function is intact. Here we report that AC3-/- mice cannot detect mouse milk, urine, or mouse pheromones. Inter-male aggressiveness and male sexual behaviors are absent in AC3-/- mice. Furthermore, adenylyl cyclase activity in membranes prepared from the MOE of wild-type mice, but not AC3-/- mice, is stimulated by 2-heptanone, a mouse pheromone. We conclude that signaling through AC3 in the MOE is obligatory for male sexual behavior, male-male aggressiveness, and the detection of some pheromones.

Phosphodiesterase 3 and 5 and cyclic nucleotide-gated ion channel expression in rat trigeminovascular system

Activation of the trigeminovascular pain signalling system appears involved in migraine pathophysiology. However, the molecular mechanisms are only partially known. Stimulation of cAMP and cGMP production as well as inhibition of their breakdown induce migraine-like headache. Additionally, migraine may be associated with mutations in ion channels. The aim of the present study was to describe the expression of phosphodiesterase 3 (PDE3) and 5 (PDE5) and cyclic nucleotide-gated ion channels (CNG) in cerebral arteries, meninges, and the trigeminal ganglion. mRNA for PDE and CNG was determined in the rat middle cerebral artery, basilar artery, trigeminal ganglion, and dura mater using real-time PCR. PDE and CNG proteins were identified using Western blot. For comparison, rat aorta and mesenteric artery were analysed. PDE3A, PDE3B, and PDE5A mRNA were detected in all tissues examined except for PDE3A mRNA in dura mater and the trigeminal ganglion. PDE5A and PDE3A protein expression was present in both cerebral and peripheral arteries, whereas PDE3B protein was present only in the cerebral arteries. The CNGA4 and B1 subunit mRNAs were detected in cerebral arteries and CNGA2 also in the mesenteric artery. CNGA2 and A3 proteins were found in cerebral arteries and dura and CNGA1, CNGA2 and CNGA3 in the trigeminal ganglion. In conclusion, PDE3A, PDE3B, PDE5A, and five CNG subunits were expressed in several components of the trigeminovascular system of the rat. This suggests that modulation of cAMP and cGMP levels by PDE and activation of CNG may play a role in trigeminovascular pain signalling leading to migraine headache.

Interaction between prostaglandin E2 and l-cis-diltiazem, a specific blocker of cyclic nucleotide gated channels in bovine aortic endothelial cells

Prostaglandins are known to transduce their signals via 7 transmembrane prostanoid receptors, which typically signal through coupling to G proteins and downstream second messenger molecules and protein kinase activation. Recently we have shown that cyclic nucleotides affect prostaglandins binding to bovine aortic endothelial cells independent of protein kinases. Here we show that incubation of bovine aortic endothelial cells with permeable analogs of cAMP or cGMP leads to a rapid and reversible reduction in PGE(2) binding to the cells. Since cyclic nucleotides are known modulators of cyclic nucleotide gated channels, we examined the effect of a specific cyclic nucleotide gated channel blocker l-cis-diltiazem on prostaglandin E(2) (PGE(2)) binding to bovine aortic endothelial cells. L-cis-diltiazem is shown to displace PGE(2) binding to bovine aortic endothelial cells in a dose dependent manner. In addition the effect of PGE(2) and l-cis-diltiazem on thapsigargin induced calcium elevation in the cells was compared. Both agents reduced in bovine aortic endothelial cells the thapsigargin induced calcium elevation by about half. PGE(2) also retarded the time course of the response to thapsigargin. Simultaneous treatment of the cells with both PGE(2) and l-cis-diltiazem did not yield an inhibitory effect beyond that observed with l-cis-diltiazem alone. Together our data point at the cyclic nucleotide gated channels as a feasible candidate for association with the PGE(2) binding site in bovine aortic endothelial cells.

A conserved tripeptide in CNG and HCN channels regulates ligand gating by controlling C-terminal oligomerization

Cyclic nucleotides directly enhance the opening of the tetrameric CNG and HCN channels, although the mechanism remains unclear. We examined why HCN and certain CNG subunits form functional homomeric channels, whereas other CNG subunits only function in heteromeric channels. The "defect" in the CNGA4 subunit that prevents its homomeric expression was localized to its C-linker, which connects the transmembrane domain to the binding domain and contains a tripeptide that decreases the efficacy of ligand gating. Remarkably, replacement of the homologous HCN tripeptide with the CNGA4 sequence transformed cAMP into an inverse agonist that inhibits HCN channel opening. Using analytical ultracentrifugation, we identified the structural basis for this gating switch: whereas cAMP normally enhances the assembly of HCN C-terminal domains into a tetrameric gating ring, inclusion of the CNGA4 tripeptide reversed this action so that cAMP now causes gating ring disassembly. Thus, ligand gating depends on the dynamic oligomerization of C-terminal binding domains.

Innovative techniques and applications in histochemistry and cell biology

Recent studies documenting novel histochemical methods and applications in cell biology and in other areas of the life sciences have again rendered insights into structure and functions of tissues, cells, and cellular components to the level of proteins and genes. Particularly, sophisticated microscopic techniques have proved to be able to significantly advance our knowledge. Findings of recent investigations representing this progress are summarized in the present review.