Regulation of cardiac and smooth muscle Ca(2+) channels (Ca(V)1.2a,b) by protein kinases

BK Channels in Tail Artery Vascular Smooth Muscle Cells of Normotensive (WKY) and Hypertensive (SHR) Rats Possess Similar Calcium Sensitivity But Different Responses to the Vasodilator Iloprost

It has been reported that, in the spontaneously hypertensive rat (SHR) model of hypertension, different components of the G-protein/adenylate cyclase (AC)/Calcium-activated potassium channel of high conductance (BK) channel signaling pathway are altered differently. In the upstream part of the pathway (G-protein/AC), a comparatively low efficacy has been established, whereas downstream BK currents seem to be increased. Thus, the overall performance of this signaling pathway in SHR is elusive. For a better understanding, we focused on one aspect, the direct targeting of the BK channel by the G-protein/AC pathway and tested the hypothesis that the comparatively low AC pathway efficacy in SHR results in a reduced agonist-induced stimulation of BK currents. This hypothesis was investigated using freshly isolated smooth muscle cells from WKY and SHR rat tail artery and the patch-clamp technique. It was observed that: (1) single BK channels have similar current-voltage relationships, voltage-dependence and calcium sensitivity; (2) BK currents in cells with a strong buffering of the BK channel activator calcium have similar current-voltage relationships; (3) the iloprost-induced concentration-dependent increase of the BK current is larger in WKY compared to SHR; (4) the effects of activators of the PKA pathway, the catalytic subunit of PKA and the potent and selective cAMP-analogue Sp-5,6-DCl-cBIMPS on BK currents are similar. Thus, our data suggest that the lower iloprost-induced stimulation of the BK current in freshly isolated rat tail artery smooth muscle cells from SHR compared with WKY is due to the lower efficacy of upstream elements of the G-Protein/AC/BK channel pathway.

Differential involvement of cAMP/PKA-, PLC/PKC- and Ca2+/calmodulin-dependent pathways in GnRH-induced prolactin secretion and gene expression in grass carp pituitary cells

Gonadotropin-releasing hormone (GnRH) is a key stimulator for gonadotropin secretion in the pituitary and its pivotal role in reproduction is well conserved in vertebrates. In fish models, GnRH can also induce prolactin (PRL) release, but little is known for the corresponding effect on PRL gene expression as well as the post-receptor signalling involved. Using grass carp as a model, the functional role of GnRH and its underlying signal transduction for PRL regulation were examined at the pituitary level. Using laser capture microdissection coupled with RT-PCR, GnRH receptor expression could be located in carp lactotrophs. In primary cell culture prepared from grass carp pituitaries, the native forms of GnRH, GnRH2 and GnRH3, as well as the GnRH agonist [D-Arg6, Pro9, NEt]-sGnRH were all effective in elevating PRL secretion, PRL mRNA level, PRL cell content and total production. In pituitary cells prepared from the rostral pars distalis, the region in the carp pituitary enriched with lactotrophs, GnRH not only increased cAMP synthesis with parallel CREB phosphorylation and nuclear translocation but also induced a rapid rise in cytosolic Ca2+ by Ca2+ influx via L-type voltage-sensitive Ca2+ channel (VSCC) with subsequent CaM expression and NFAT2 dephosphorylation. In carp pituitary cells prepared from whole pituitaries, GnRH-induced PRL secretion was reduced/negated by inhibiting cAMP/PKA, PLC/PKC and Ca2+/CaM/CaMK-II pathways but not the signalling events via IP3 and CaN/NFAT. The corresponding effect on PRL mRNA expression, however, was blocked by inhibiting cAMP/PKA/CREB/CBP and Ca2+/CaM/CaN/NFAT2 signalling but not PLC/IP3/PKC pathway. At the pituitary cell level, activation of cAMP/PKA pathway could also induce CaM expression and Ca2+ influx via VSCC with parallel rises in PRL release and gene expression in a Ca2+/CaM-dependent manner. These findings, as a whole, suggest that the cAMP/PKA-, PLC/PKC- and Ca2+/CaM-dependent cascades are differentially involved in GnRH-induced PRL secretion and PRL transcript expression in carp lactotrophs. During the process, a functional crosstalk between the cAMP/PKA- and Ca2+/CaM-dependent pathways may occur with PRL release linked with CaMK-II and PKC activation and PRL gene transcription caused by nuclear action of CREB/CBP and CaN/NFAT2 signalling.

Pacemaker Channels and the Chronotropic Response in Health and Disease

Loss or dysregulation of the normally precise control of heart rate via the autonomic nervous system plays a critical role during the development and progression of cardiovascular disease-including ischemic heart disease, heart failure, and arrhythmias. While the clinical significance of regulating changes in heart rate, known as the chronotropic effect, is undeniable, the mechanisms controlling these changes remain not fully understood. Heart rate acceleration and deceleration are mediated by increasing or decreasing the spontaneous firing rate of pacemaker cells in the sinoatrial node. During the transition from rest to activity, sympathetic neurons stimulate these cells by activating β-adrenergic receptors and increasing intracellular cyclic adenosine monophosphate. The same signal transduction pathway is targeted by positive chronotropic drugs such as norepinephrine and dobutamine, which are used in the treatment of cardiogenic shock and severe heart failure. The cyclic adenosine monophosphate-sensitive hyperpolarization-activated current (If) in pacemaker cells is passed by hyperpolarization-activated cyclic nucleotide-gated cation channels and is critical for generating the autonomous heartbeat. In addition, this current has been suggested to play a central role in the chronotropic effect. Recent studies demonstrate that cyclic adenosine monophosphate-dependent regulation of HCN4 (hyperpolarization-activated cyclic nucleotide-gated cation channel isoform 4) acts to stabilize the heart rate, particularly during rapid rate transitions induced by the autonomic nervous system. The mechanism is based on creating a balance between firing and recently discovered nonfiring pacemaker cells in the sinoatrial node. In this way, hyperpolarization-activated cyclic nucleotide-gated cation channels may protect the heart from sinoatrial node dysfunction, secondary arrhythmia of the atria, and potentially fatal tachyarrhythmia of the ventricles. Here, we review the latest findings on sinoatrial node automaticity and discuss the physiological and pathophysiological role of HCN pacemaker channels in the chronotropic response and beyond.

Diversity of cells and signals in the cardiovascular system

This white paper is the outcome of the seventh UC Davis Cardiovascular Research Symposium on Systems Approach to Understanding Cardiovascular Disease and Arrhythmia. This biannual meeting aims to bring together leading experts in subfields of cardiovascular biomedicine to focus on topics of importance to the field. The theme of the 2022 Symposium was 'Cell Diversity in the Cardiovascular System, cell-autonomous and cell-cell signalling'. Experts in the field contributed their experimental and mathematical modelling perspectives and discussed emerging questions, controversies, and challenges in examining cell and signal diversity, co-ordination and interrelationships involved in cardiovascular function. This paper originates from the topics of formal presentations and informal discussions from the Symposium, which aimed to develop a holistic view of how the multiple cell types in the cardiovascular system integrate to influence cardiovascular function, disease progression and therapeutic strategies. The first section describes the major cell types (e.g. cardiomyocytes, vascular smooth muscle and endothelial cells, fibroblasts, neurons, immune cells, etc.) and the signals involved in cardiovascular function. The second section emphasizes the complexity at the subcellular, cellular and system levels in the context of cardiovascular development, ageing and disease. Finally, the third section surveys the technological innovations that allow the interrogation of this diversity and advancing our understanding of the integrated cardiovascular function and dysfunction.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

The Importance of Integrated Regulation Mechanism of Coronary Microvascular Function for Maintaining the Stability of Coronary Microcirculation: An Easily Overlooked Perspective

Coronary microvascular dysfunction (CMD) refers to a group of disorders affecting the structure and function of coronary microcirculation and is associated with an increased risk of major adverse cardiovascular events. At present, great progress has been made in the diagnosis of CMD, but there is no specific treatment for it because of the complexity of CMD pathogenesis. Vascular dysfunction is one of the important causes of CMD, but previous reviews mostly considered microvascular dysfunction as a whole abnormality so the obtained conclusions are skewed. The coronary microvascular function is co-regulated by multiple mechanisms, and the mechanisms by which microvessels of different luminal diameters are regulated vary. The main purpose of this review is to revisit the mechanisms by which coronary microvessels at different diameters regulate coronary microcirculation through integrated sequential activation and briefly discuss the pathogenesis, diagnosis, and treatment progress of CMD from this perspective.

Mechanisms of Vascular CaV1.2 Channel Regulation During Diabetic Hyperglycemia

Diabetes is a leading cause of disability and mortality worldwide. A major underlying factor in diabetes is the excessive glucose levels in the bloodstream (e.g., hyperglycemia). Vascular complications directly result from this metabolic abnormality, leading to disabling and life-threatening conditions. Dysfunction of vascular smooth muscle cells is a well-recognized factor mediating vascular complications during diabetic hyperglycemia. The function of vascular smooth muscle cells is exquisitely controlled by different ion channels. Among the ion channels, the L-type CaV1.2 channel plays a key role as it is the main Ca2+ entry pathway regulating vascular smooth muscle contractile state. The activity of CaV1.2 channels in vascular smooth muscle is altered by diabetic hyperglycemia, which may contribute to vascular complications. In this chapter, we summarize the current understanding of the regulation of CaV1.2 channels in vascular smooth muscle by different signaling pathways. We place special attention on the regulation of CaV1.2 channel activity in vascular smooth muscle by a newly uncovered AKAP5/P2Y11/AC5/PKA/CaV1.2 axis that is engaged during diabetic hyperglycemia. We further describe the pathophysiological implications of activation of this axis as it relates to myogenic tone and vascular reactivity and propose that this complex may be targeted for developing therapies to treat diabetic vascular complications.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Cellular cross talk between epicardial fat and cardiovascular risk

A variety of fat compartments have several local and systemic effect and play a crucial role in the maintenance of health and development of disease. For the past few years, special attention has been paid to epicardial fat. It is the visceral fat compartment of the heart and has several local and systemic effects. It can perform a role in the development of cardiometabolic risk. The epicardial adipose tissue (EAT) is a unique and multifunctional fat compartment of the heart. It is located between the myocardium and the visceral pericardium. During normal physiological conditions, the EAT has metabolic, thermogenic, and mechanical (cardioprotective) characteristics. The EAT can produce several adipocytokines and chemokines depending on microenvironments. It can influence through paracrine and vasocrine mechanism and participate in the development and progression of cardiovascular (CVS) diseases. In addition, metabolic disease leads to changes in both thickness and volume of the EAT, and it can modify the structure and the function of heart. It has been associated with various CVS diseases such as, cardiomyopathy, atrial fibrillation, and coronary artery disease. Therefore, EAT is a potential therapeutic target for CVS risk.

Vascular CaV1.2 channels in diabetes

Diabetic vasculopathy is a significant cause of morbidity and mortality in the diabetic population. Hyperglycemia, one of the central metabolic abnormalities in diabetes, has been associated with vascular dysfunction due to endothelial cell damage. However, studies also point toward vascular smooth muscle as a locus for hyperglycemia-induced vascular dysfunction. Emerging evidence implicates hyperglycemia-induced regulation of vascular L-type Ca²⁺ channels Ca_V1.2 as a potential mechanism for vascular dysfunction during diabetes. This chapter summarizes our current understanding of vascular Ca_V1.2 channels and their regulation during physiological and hyperglycemia/diabetes conditions. We will emphasize the role of Ca_V1.2 in vascular smooth muscle, the effects of elevated glucose on Ca_V1.2 function, and the mechanisms underlying its dysregulation in hyperglycemia and diabetes. We conclude by examining future directions and gaps in knowledge regarding Ca_V1.2 regulation in health and during diabetes.

KATP channels in lymphatic function

KATP channels function as negative regulators of active lymphatic pumping and lymph transport. This review summarizes and critiques the evidence for the expression of specific KATP channel subunits in lymphatic smooth muscle and endothelium, the roles that they play in normal lymphatic function, and their possible involvement in multiple diseases, including metabolic syndrome, lymphedema, and Cantú syndrome. For each of these topics, suggestions are made for directions for future research.

4-[1-Ethyl-1-methylhexy]-phenol induces apoptosis and interrupts Ca2+ homeostasis via ROS pathway in Sertoli TM4 cells

Biological effect of an individual nonylphenol (NP) isomer extremely relies upon the side chain structure. This research was designed to evaluate the impact of NP isomer, 4-[1-ethyl-1-methylhexy]-phenol (NP₆₅), on Sertoli cells in vitro. Sertoli TM4 cells were exposed to various concentration (0, 0.1, 1, 10, or 20 μM) of NP₆₅ for 24 h, and the outcomes indicated that treatment of NP₆₅ induced reactive oxygen species (ROS) generation, oxidative stress, and apoptosis for Sertoli TM4 cells. In addition, it was found that NP₆₅ exposure affected homeostasis of Ca²⁺ in Sertoli TM4 cells by increasing cytoplasm [Ca²⁺]i, inhibiting Ca²⁺-ATPase activity and decreasing cyclic adenosine monophosphate (cAMP) concentration. Pretreatment with ROS scavenger, N-acetylcysteine (NAC), attenuated NP₆₅-induced oxidative stress as well as apoptosis for TM4 cells. Furthermore, NAC blocked NP₆₅-induced disorders of Ca²⁺ homeostasis by attenuating the growth of intracellular [Ca²⁺]i and the inhibition of Ca²⁺-ATPase and cAMP activities. Thus, we have demonstrated that NP₆₅ induced apoptosis as well as acted as a potent inhibitor of Ca²⁺-ATPase activity and resulted in disorder of Ca²⁺ homeostasis in Sertoli TM4 cells; ROS participated in the process. Our results supported the view that oxidative stress acted an essential role within the development of apoptosis and Ca²⁺ overload in TM4 cells as a consequence of NP₆₅ stimulation.

Endothelin-1 induces lipolysis through activation of the GC/cGMP/Ca2+/ERK/CaMKIII pathway in 3T3-L1 adipocytes

Endothelin-1 (ET-1) is a potent vasoconstrictive peptide produced and secreted mainly by endothelial cells. Recent studies indicate that ET-1 can regulate lipid metabolism, which may increase the risk of insulin resistance. Our previous studies revealed that ET-1 induced lipolysis in adipocytes, but the underlying mechanisms were unclear. 3T3-L1 adipocytes were used to investigate the effect of ET-1 on lipolysis and the underlying mechanisms. Glycerol levels in the incubation medium and hormone-sensitive lipase (HSL) phosphorylation were used as indices for lipolysis. ET-1 significantly increased HSL phosphorylation and lipolysis, which were completely inhibited by ERK inhibitor (PD98059) and guanylyl cyclase (GC) inhibitor (LY83583). LY83583 reduced ET-1-induced ERK phosphorylation. A Ca2+-free medium and PLC inhibitor caused significant decreases in ET-1-induced lipolysis as well as ERK and HSL phosphorylation, and IP3 receptor activator (D-IP3) increased lipolysis. ET-1 increased cGMP production, which was not affected by depletion of extracellular Ca2+. On the other hand, LY83583 diminished the ET-1-induced Ca2+ influx. Transient receptor potential vanilloid-1 (TRPV-1) antagonist and shRNA partially inhibited ET-1-induced lipolysis. ET-1-induced lipolysis was completely suppressed by CaMKIII inhibitor (NH-125). These results indicate that ET-1 stimulates extracellular Ca2+ entry and activates the intracellular PLC/IP3/Ca2+ pathway through a cGMP-dependent pathway. The increased cytosolic Ca2+ that results from ET-1 treatment stimulates ERK and HSL phosphorylation, which subsequently induces lipolysis. ET-1 induces HSL phosphorylation and lipolysis via the GC/cGMP/Ca2+/ERK/CaMKIII signaling pathway in 3T3-L1 adipocytes.

Large-conductance calcium-activated K+ channels, rather than KATP channels, mediate the inhibitory effects of nitric oxide on mouse lymphatic pumping

BACKGROUND AND PURPOSE

K_ATP channels are negative regulators of lymphatic vessel excitability and contractility and are proposed to be targets for immune cell products that inhibit lymph transport. Previous studies in rat and guinea pig mesenteric lymphatics found that NO-mediated inhibition of lymphatic contraction was prevented or reversed by the K_ATP channel inhibitor, glibenclamide. We revisited this hypothesis using mouse lymphatic vessels and K_ATP channel knockout mice.

EXPERIMENTAL APPROACH

Mouse popliteal lymphatics were isolated, and contractility was assessed using pressure myography. K⁺ channel expression was determined by PCR analysis of FACS-purified lymphatic smooth muscle cells.

KEY RESULTS

The NO-producing agonist, ACh, and the NO donor, NONOate, both produced dose-dependent inhibition of spontaneous lymphatic contractions that were blocked by the soluble GC inhibitor, ODQ, or the PKG inhibitor, Rp-8-Br-PET-cGMPS. Surprisingly, the inhibitory effects of both were preserved in K_ir 6.1^-/- vessels, suggesting that K_ATP channels did not mediate NO-induced responses. We hypothesized a role for BK channels, given their prominence in arterial smooth muscle. Indeed, BK channels were expressed in mouse lymphatic smooth muscle and NS11021 (a BK channel activator) caused dilation and reduced contraction frequency, whereas iberiotoxin and penitrem A (BK channel inhibitors) produced right-ward shifts in NONOate concentration-response curves.

CONCLUSION AND IMPLICATIONS

Inhibition of mouse lymphatic contractions by NO primarily involves activation of BK channels, rather than K_ATP channels. Thus, BK channels are a potential target for therapeutic reversal of lymph pump inhibition by NO generated by immune cell activation of iNOS in chronic lymphoedema.

LncRNA ENSMUST00000155383 is Involved in the Improvement of DPP-4 Inhibitor MK-626 on Vascular Endothelial Function by Modulating Cacna1c-Mediated Ca2+ Influx in Hypertensive Mice

Objective: This study investigated the protective effects of dipeptidyl peptidase-4 inhibitor MK-626 on vascular endothelial function by regulating lncRNAs in hypertensive vasculature.

Methods: Angiotensin Ⅱ (Ang Ⅱ)-loaded osmotic pumps were implanted in mice with or without MK-626 administration. GLP-1 levels in plasma were measured by ELISA. Aortic rings were suspended in myograph for tension measurement. Microarray was performed to analyze lncRNA and mRNA expression profiles. Protein expression and phosphorylation were examined by Western blot. The differentially expressed (DE)-genes were validated by qRT-PCR. The intracellular Ca²⁺ concentration was detected by laser confocal system.

Results: MK-626 elevated plasma GLP-1 level, increased eNOS phosphorylation, improved endothelium-dependent relaxations, and reduced systolic blood pressure in Ang Ⅱ-induced hypertensive mice. Microarray revealed the dysregulations of 723 lncRNAs and 742 mRNAs were reversed by MK-626 in hypertensive mouse aortae. qRT-PCR validation showed that 13 DE-lncRNAs and eight dysregulated mRNAs in both hypertensive mouse aortae and mouse aortic endothelial cells (MAECs) were rescued by MK-626. Among them, four mRNAs (Cacna1C, Itgav, Itga8, and Npnt) were co-expressed with lncRNA ENSMUST00000155383. Cacna1C protein expression was reduced in the ECs but was elevated in smooth muscle cells from Ang Ⅱ-infused mice, which were both reversed by MK-626. Knockdown of lncRNA ENSMUST00000155383 suppressed the increased Cacna1c protein and mRNA expression, elevated Ca²⁺ level, and enhanced eNOS phosphorylation induced by MK-626 in the hypertensive mouse ECs.

Conclusion: The dysregulations of lncRNA ENSMUST00000155383-associated genes might play crucial roles in hypertension-induced endothelial dysfunction through affecting calcium pathway. MK-626 might ameliorate endothelial dysfunction by upregulating lncRNA ENSMUST00000155383, enhancing Ca²⁺ concentration, and subsequently restoring eNOS activity in hypertension.

Diagnosis and prevention of the vasodepressor type of neurally mediated syncope in Japanese patients

We investigated circulatory dynamics in patients with vasodepressor type neurally mediated syncope (VT-NMS) by performing high-resolution Holter electrocardiography and a correlation analysis of changes in adenylate cyclase activity, blood pressure, and pulse during the head-up tilt test. Holter electrocardiography was performed for 30 patients. Adenylate cyclase activity was evaluated in lymphocytes from blood samples taken at rest and during the head-up tilt test. There was no change in autonomic nerve fluctuation during electrocardiography in VT-NMS patients, but our results showed a significant difference in blood pressure and adenylate cyclase activity between VT-NMS patients and healthy volunteers; the systolic blood pressure of VT-NMS patients decreased after 5 min, while at 10 min, the adenylate cyclase activity was the highest (0.53%) and the systolic blood pressure was the lowest (111.8 mm Hg). Pulse rates increased after 10 min. VT-NMS patients showed higher blood pressure, pulse rate, and adenylate cyclase activity during the tilt test than did healthy volunteers. In patients with syncope, standing for longer than 10 minutes may increase the risk of VT-NMS. From our results, we consider it likely that high systolic blood pressure and adenylate cyclase activity at rest cause fainting in VT-NMS patients. Our findings may be helpful for identifying individuals with a high risk of developing NMS in the healthy population.

Potential Benefits of Flavonoids on the Progression of Atherosclerosis by Their Effect on Vascular Smooth Muscle Excitability

Flavonoids are a group of secondary metabolites derived from plant-based foods, and they offer many health benefits in different stages of several diseases. This review will focus on their effects on ion channels expressed in vascular smooth muscle during atherosclerosis. Since ion channels can be regulated by redox potential, it is expected that during the onset of oxidative stress-related diseases, ion channels present changes in their conductive activity, impacting the progression of the disease. A typical oxidative stress-related condition is atherosclerosis, which involves the dysfunction of vascular smooth muscle. We aim to present the state of the art on how redox potential affects vascular smooth muscle ion channel function and summarize if the benefits observed in this disease by using flavonoids involve restoring the ion channel activity.

The Calcium Signaling Mechanisms in Arterial Smooth Muscle and Endothelial Cells

The contractile state of resistance arteries and arterioles is a crucial determinant of blood pressure and blood flow. Physiological regulation of arterial contractility requires constant communication between endothelial and smooth muscle cells. Various Ca²⁺ signals and Ca²⁺ -sensitive targets ensure dynamic control of intercellular communications in the vascular wall. The functional effect of a Ca²⁺ signal on arterial contractility depends on the type of Ca²⁺ -sensitive target engaged by that signal. Recent studies using advanced imaging methods have identified the spatiotemporal signatures of individual Ca²⁺ signals that control arterial and arteriolar contractility. Broadly speaking, intracellular Ca²⁺ is increased by ion channels and transporters on the plasma membrane and endoplasmic reticular membrane. Physiological roles for many vascular Ca²⁺ signals have already been confirmed, while further investigation is needed for other Ca²⁺ signals. This article focuses on endothelial and smooth muscle Ca²⁺ signaling mechanisms in resistance arteries and arterioles. We discuss the Ca²⁺ entry pathways at the plasma membrane, Ca²⁺ release signals from the intracellular stores, the functional and physiological relevance of Ca²⁺ signals, and their regulatory mechanisms. Finally, we describe the contribution of abnormal endothelial and smooth muscle Ca²⁺ signals to the pathogenesis of vascular disorders. © 2021 American Physiological Society. Compr Physiol 11:1831-1869, 2021.

Cellular and molecular effects of hyperglycemia on ion channels in vascular smooth muscle

Diabetes affects millions of people worldwide. This devastating disease dramatically increases the risk of developing cardiovascular disorders. A hallmark metabolic abnormality in diabetes is hyperglycemia, which contributes to the pathogenesis of cardiovascular complications. These cardiovascular complications are, at least in part, related to hyperglycemia-induced molecular and cellular changes in the cells making up blood vessels. Whereas the mechanisms mediating endothelial dysfunction during hyperglycemia have been extensively examined, much less is known about how hyperglycemia impacts vascular smooth muscle function. Vascular smooth muscle function is exquisitely regulated by many ion channels, including several members of the potassium (K+) channel superfamily and voltage-gated L-type Ca2+ channels. Modulation of vascular smooth muscle ion channels function by hyperglycemia is emerging as a key contributor to vascular dysfunction in diabetes. In this review, we summarize the current understanding of how diabetic hyperglycemia modulates the activity of these ion channels in vascular smooth muscle. We examine underlying mechanisms, general properties, and physiological relevance in the context of myogenic tone and vascular reactivity.

AKAP5 complex facilitates purinergic modulation of vascular L-type Ca2+ channel CaV1.2

The L-type Ca2+ channel CaV1.2 is essential for arterial myocyte excitability, gene expression and contraction. Elevations in extracellular glucose (hyperglycemia) potentiate vascular L-type Ca2+ channel via PKA, but the underlying mechanisms are unclear. Here, we find that cAMP synthesis in response to elevated glucose and the selective P2Y11 agonist NF546 is blocked by disruption of A-kinase anchoring protein 5 (AKAP5) function in arterial myocytes. Glucose and NF546-induced potentiation of L-type Ca2+ channels, vasoconstriction and decreased blood flow are prevented in AKAP5 null arterial myocytes/arteries. These responses are nucleated via the AKAP5-dependent clustering of P2Y11/ P2Y11-like receptors, AC5, PKA and CaV1.2 into nanocomplexes at the plasma membrane of human and mouse arterial myocytes. Hence, data reveal an AKAP5 signaling module that regulates L-type Ca2+ channel activity and vascular reactivity upon elevated glucose. This AKAP5-anchored nanocomplex may contribute to vascular complications during diabetic hyperglycemia.

Fine tuning by protein kinases of CaV1.2 channel current in rat tail artery myocytes

Seventeen compounds, rather selective, direct or indirect inhibitors and activators of PKA, PKG, and PKC, were analysed for effects on vascular Ca_V1.2 channel current (I_Ca1.2) by using the patch-clamp technique in single rat tail artery myocytes. The aim was to investigate how PKs regulate I_Ca1.2 and disclose any unexpected modulation of Ca_V1.2 channel function by these agents. The cAMP analogues 8-Br-cAMP and 6-Bnz-cAMP partially reduced I_Ca1.2 in dialysed cells, while weakly increasing it under the perforated configuration. The β-adrenoceptor agonist isoproterenol and the adenylate cyclase activator forskolin concentration-dependently increased I_Ca1.2; this effect was reversed by PKA inhibitors H-89 and KT5720, but not by PKI 6-22. The cGMP analogue 8-Br-cGMP, similarly to the NO-donor SNP, moderately reduced I_Ca1.2, this effect being reversed to a slight stimulation under the perforated configuration. Among PKG inhibitors, Rp-8-Br-PET-cGMPS decreased current amplitude in a concentration-dependent manner while Rp-8-Br-cGMPS was ineffective. The non-specific phosphodiesterase inhibitor IBMX increased I_Ca1.2, while H-89, KT5720, and PKI 6-22 antagonized this effect. The PKC activator PMA, but not the diacylglycerol analogue OAG, stimulated I_Ca1.2 in a concentration-dependent manner; conversely, the PKCα inhibitor Gö6976 markedly reduced basal I_Ca1.2 and, similarly to the PKCδ (rottlerin) and PKCε translocation inhibitors antagonised PMA-induced current stimulation. The ensemble of findings indicates that the stimulation of cAMP/PKA, in spite of the paradoxical effect of both 8-Br-cAMP and 6-Bnz-cAMP, or PKC pathways enhanced, while that of cGMP/PKG weakly inhibited I_Ca1.2 in rat tail artery myocytes. Since Rp-8-Br-PET-cGMPS and Gö6976 appeared to block directly Ca_V1.2 channel, their docking to the channel protein was investigated. Both compounds appeared to bind the α_1C subunit in a region involved in Ca_V1.2 channel inactivation, forming an interaction network comparable to that of Ca_V1.2 channel blockers. Therefore, caution should accompany the use of these agents as pharmacological tools to elucidate the mechanism of action of drugs on vascular preparations.

Intracellular O-linked glycosylation directly regulates cardiomyocyte L-type Ca2+ channel activity and excitation-contraction coupling

Cardiomyocyte L-type Ca²⁺ channels (Ca_vs) are targets of signaling pathways that modulate channel activity in response to physiologic stimuli. Ca_v regulation is typically transient and beneficial but chronic stimulation can become pathologic; therefore, gaining a more complete understanding of Ca_v regulation is of critical importance. Intracellular O-linked glycosylation (O-GlcNAcylation), which is the result of two enzymes that dynamically add and remove single N-acetylglucosamines to and from intracellular serine/threonine residues (OGT and OGA respectively), has proven to be an increasingly important post-translational modification that contributes to the regulation of many physiologic processes. However, there is currently no known role for O-GlcNAcylation in the direct regulation of Ca_v activity nor is its contribution to cardiac electrical signaling and EC coupling well understood. Here we aimed to delineate the role of O-GlcNAcylation in regulating cardiomyocyte L-type Ca_v activity and its subsequent effect on EC coupling by utilizing a mouse strain possessing an inducible cardiomyocyte-specific OGT-null-transgene. Ablation of the OGT-gene in adult cardiomyocytes (OGTKO) reduced OGT expression and O-GlcNAcylation by > 90%. Voltage clamp recordings indicated an ~ 40% reduction in OGTKO Ca_v current (I_Ca), but with increased efficacy of adrenergic stimulation, and Ca_v steady-state gating and window current were significantly depolarized. Consistently, OGTKO cardiomyocyte intracellular Ca²⁺ release and contractility were diminished and demonstrated greater beat-to-beat variability. Additionally, we show that the Ca_v α1 and β2 subunits are O-GlcNAcylated while α2δ1 is not. Echocardiographic analyses indicated that the reductions in OGTKO cardiomyocyte Ca²⁺ handling and contractility were conserved at the whole-heart level as evidenced by significantly reduced left-ventricular contractility in the absence of hypertrophy. The data indicate, for the first time, that O-GlcNAc signaling is a critical and direct regulator of cardiomyocyte I_Ca achieved through altered Ca_v expression, gating, and response to adrenergic stimulation; these mechanisms have significant implications for understanding how EC coupling is regulated in health and disease.

Analysis of the source of aggressiveness in gamecocks

Although the fighting behaviour in gamecocks has evolved because of artificial selection, it is unknown whether the selection for aggressiveness affects neurotransmitter levels in the avian central nervous system. We sought to identify the source and origin of this trait. We collected the brain samples from 6 female Shamo gamecocks and 5 Shaver Brown chickens (control; bred for egg production). The midbrain levels of norepinephrine (NE) were significantly higher in Shamo gamecocks (P = 0.0087) than in the controls. Moreover, alleles encoding adrenergic receptors differed between the breeds in terms of response to NE. Gene mutations specific to Shamo and potentially associated with fighting behaviour were in sites T440N of ADRα1D; V296I of ADRα2A; and T44I, Q232R, and T277M of ADRβ2. The evolutionary analysis indicated that the ADRβ2 (T44I and Q232R) mutations were heritable in all Galliformes, whereas the T440N mutation of ADRα1D and V296I mutations of ADRα2A were unique to Shamo and originated by artificial selection. A high NE level may confer a selective advantage by enabling gamecocks to be aggressive and pain tolerant. Therefore, the strong fighting behaviour of Shamo has resulted from a combination of naturally inherited and mutant genes derived by artificial selection.

Ion channels as effectors of cyclic nucleotide pathways: Functional relevance for arterial tone regulation

Numerous mediators and drugs regulate blood flow or arterial pressure by acting on vascular tone, involving cyclic nucleotide intracellular pathways. These signals lead to regulation of several cellular effectors, including ion channels that tune cell membrane potential, Ca²⁺ influx and vascular tone. The characterization of these vasocontrictive or vasodilating mechanisms has grown in complexity due to i) the variety of ion channels that are expressed in both vascular endothelial and smooth muscle cells, ii) the heterogeneity of responses among the various vascular beds, and iii) the number of molecular mechanisms involved in cyclic nucleotide signalling in health and disease. This review synthesizes key data from literature that highlight ion channels as physiologically relevant effectors of cyclic nucleotide pathways in the vasculature, including the characterization of the molecular mechanisms involved. In smooth muscle cells, cation influx or chloride efflux through ion channels are associated with vasoconstriction, whereas K⁺ efflux repolarizes the cell membrane potential and mediates vasodilatation. Both categories of ion currents are under the influence of cAMP and cGMP pathways. Evidence that some ion channels are influenced by CN signalling in endothelial cells will also be presented. Emphasis will also be put on recent data touching a variety of determinants such as phosphodiesterases, EPAC and kinase anchoring, that complicate or even challenge former paradigms.

Control of Motility in the Internal Anal Sphincter

The internal anal sphincter (IAS) plays an important role in the maintenance of fecal continence since it generates tone and is responsible for > 70% of resting anal pressure. During normal defecation the IAS relaxes. Historically, tone generation in gastrointestinal muscles was attributed to mechanisms arising directly from smooth muscle cells, ie, myogenic activity. However, slow waves are now known to play a fundamental role in regulating gastrointestinal motility and these electrical events are generated by the interstitial cells of Cajal. Recently, interstitial cells of Cajal, as well as slow waves, have also been identified in the IAS making them viable candidates for tone generation. In this review we discuss four different mechanisms that likely contribute to tone generation in the IAS. Three of these involve membrane potential, L-type Ca²⁺ channels and electromechanical coupling (ie, summation of asynchronous phasic activity, partial tetanus, and window current), whereas the fourth involves the regulation of myofilament Ca²⁺ sensitivity. Contractile activity in the IAS is also modulated by sympathetic motor neurons that significantly increase tone and anal pressure, as well as inhibitory motor neurons (particularly nitrergic and vasoactive intestinal peptidergic) that abolish contraction and assist with normal defecation. Alterations in IAS motility are associated with disorders such as fecal incontinence and anal fissures that significantly decrease the quality of life. Understanding in greater detail how tone is regulated in the IAS is important for developing more effective treatment strategies for these debilitating defecation disorders.

Neurally mediated syncope diagnosis based on adenylate cyclase activity in Japanese patients

The study aims to clarify the mechanism in patients with neurally mediated syncope (NMS), focusing on the adenylate cyclase (AC) activity level in lymphocytes. This study included 40 subjects: 22 healthy volunteers and 18 NMS patients. We investigated the changes in AC activity that occur during of syncope at rest and during the head-up tilt (HUT) test. We obtained 8 mL of blood at rest time and four times during the HUT test. Then, we measured the AC activity and the test reagent was added to the lymphocytes (10,000) and reacted for 30 min at room temperature. We were able to determine the standard value of AC activity when adrenaline (AD) and isoproterenol (IP) were added to lymphocytes. The results of our study showed one of the causes of NMS has a difference in AC activity level and classification of the patients into two different types of NMS was possible: either the vasodepressor type (VT) or mixed type (MT). At rest time, VT patients showed significantly higher AC activity (AD; 100 μM: p = 0.005, IP; 50 μM: p = 0.02) and MT patients showed significantly lower AC activity (AD; 10 μM: p = 0.02, IP; 50 μM: p = 0.004) than the average AC activity in healthy volunteers. Moreover, VT patients had significantly higher AC activity than healthy volunteers at the four points of the HUT test. MT patients had significantly lower AC activity (AD: p = 0.04 and IP: p = 0.04) than healthy volunteers at the rest time of HUT. Our study showed a significant difference in AC activities between NMS patients and healthy volunteers at rest. Therefore, a detailed NMS diagnosis can be made by examining AC activity levels in blood taken at rest time.

Synergism of myocardial β-adrenoceptor blockade and I1-imidazoline receptor-driven signaling: Kinase-phosphatase switching

Recently identified imidazoline receptors of the first type (I₁Rs) on the cardiomyocyte's sarcolemma open a new field in calcium signaling research. In particular, it is interesting to investigate their functional interaction with other well-known systems, such as β-adrenergic receptors. Here we investigated the effects of I₁Rs activation on L-type voltage-gated Ca²⁺-currents under catecholaminergic stress induced by the application of β-agonist, isoproterenol. Pharmacological agonist of I₁Rs (I₁-agonist), rilmenidine, and the putative endogenous I₁-ligand, agmatine, have been shown to effectively reduce Ca²⁺-currents potentiated by isoproterenol. Inhibitory analysis shows that the ability to suppress voltage-gated Ca²⁺-currents by rilmenidine and agmatine is fully preserved in the presence of the protein kinase A blocker (PKA), which indicates a PKA-independent mechanism of their action. The blockade of NO synthase isoforms with 7NI does not affect the intrinsic effects of agmatine and rilmenidine, which suggests NO-independent signaling pathways triggered by I₁Rs. A nonspecific serine/threonine protein phosphatase (STPP) inhibitor, calyculin A, abrogates effects of rilmenidine or agmatine on the isoproterenol-induced Ca²⁺-currents. Direct measurements of phosphatase activity in the myocardial tissues showed that activation of the I₁Rs leads to stimulation of STPP, which could be responsible for the I₁-agonist influences. Obtained data clarify peripheral effects that occur during activation of the I₁Rs under endogenous catecholaminergic stress, and can be used in clinical practice for more precise control of heart contractility in some cardiovascular pathologies.

Sarcolemmal α2-adrenoceptors in feedback control of myocardial response to sympathetic challenge

α2-adrenoceptor (α2-AR) isoforms, abundant in sympathetic synapses and noradrenergic neurons of the central nervous system, are integral in the presynaptic feed-back loop mechanism that moderates norepinephrine surges. We recently identified that postsynaptic α2-ARs, found in the myocellular sarcolemma, also contribute to a muscle-delimited feedback control capable of attenuating mobilization of intracellular Ca²⁺ and myocardial contractility. This previously unrecognized α2-AR-dependent rheostat is able to counteract competing adrenergic receptor actions in cardiac muscle. Specifically, in ventricular myocytes, nitric oxide (NO) and cGMP are the intracellular messengers of α2-AR signal transduction pathways that gauge the kinase-phosphatase balance and manage cellular Ca²⁺ handling preventing catecholamine-induced Ca²⁺ overload. Moreover, α2-AR signaling counterbalances phospholipase C - PKC-dependent mechanisms underscoring a broader cardioprotective potential under sympathoadrenergic and angiotensinergic challenge. Recruitment of such tissue-specific features of α2-AR under sustained sympathoadrenergic drive may, in principle, be harnessed to mitigate or prevent cardiac malfunction. However, cardiovascular disease may compromise peripheral α2-AR signaling limiting pharmacological targeting of these receptors. Prospective cardiac-specific gene or cell-based therapeutic approaches aimed at repairing or improving stress-protective α2-AR signaling may offer an alternative towards enhanced preservation of cardiac muscle structure and function.

Ion Channels and Intracellular Calcium Signalling in Corpus Cavernosum

The corpus cavernosum smooth muscle is important for both erection of the penis and for maintaining penile flaccidity. Most of the time, the smooth muscle cells are in a contracted state, which limits filling of the corpus sinuses with blood. Occasionally, however, they relax in a co-ordinated manner, allowing filling to occur. This results in an erection. When contractions of the corpus cavernosum are measured, it can be deduced that the muscle cells work together in a syncytium, for not only do they spontaneously contract in a co-ordinated manner, but they also synchronously relax. It is challenging to understand how they achieve this.In this review we will attempt to explain the activity of the corpus cavernosum, firstly by summarising current knowledge regarding the role of ion channels and how they influence tone, and secondly by presenting data on the intracellular Ca²⁺ signals that interact with the ion channels. We propose that spontaneous Ca²⁺ waves act as a primary event, driving transient depolarisation by activating Ca²⁺-activated Cl^- channels. Depolarisation then facilitates Ca²⁺ influx via L-type voltage-dependent Ca²⁺ channels. We propose that the spontaneous Ca²⁺ oscillations depend on Ca²⁺ release from both ryanodine- and inositol trisphosphate (IP₃)-sensitive stores and that modulation by signalling molecules is achieved mainly by interactions with the IP₃-sensitive mechanism. This pacemaker mechanism is inhibited by nitric oxide (acting through cyclic GMP) and enhanced by noradrenaline. By understanding these mechanisms better, it might be possible to design new treatments for erectile dysfunction.

Comparison of inhibitory neuromuscular transmission in the Cynomolgus monkey IAS and rectum: special emphasis on differences in purinergic transmission

KEY POINTS

Inhibitory neuromuscular transmission (NMT) was compared in the internal anal sphincter (IAS) and rectum of the Cynomolgus monkey, an animal with high gene sequence identity to humans. Nitrergic NMT was present in both muscles while purinergic NMT was limited to the rectum and VIPergic NMT to the IAS. The profile for monkey IAS more closely resembles humans than rodents. In both muscles, SK3 channels were localized to PDGFRα⁺ cells that were closely associated with nNOS⁺ /VIP⁺ nerves. Gene expression levels of P2RY subtypes were the same in IAS and rectum while KCNN expression levels were very similar. SK3 channel activation and inhibition caused faster/greater changes in contractile activity in rectum than IAS. P2Y1 receptor activation inhibited contraction in rectum while increasing contraction in IAS. The absence of purinergic NMT in the IAS may be due to poor coupling between P2Y1 receptors and SK3 channels on PDGFRα⁺ cells.

ABSTRACT

Inhibitory neuromuscular transmission (NMT) was compared in the internal anal sphincter (IAS) and rectum of the Cynomolgus monkey, an animal with a high gene sequence identity to humans. Electrical field stimulation produced nitric oxide synthase (NOS)-dependent contractile inhibition in both muscles whereas P2Y1-dependent purinergic NMT was restricted to rectum. An additional NOS-independent, α-chymotrypsin-sensitive component was identified in the IAS consistent with vasoactive intestinal peptide-ergic (VIPergic) NMT. Microelectrode recordings revealed slow NOS-dependent inhibitory junction potentials (IJPs) in both muscles and fast P2Y1-dependent IJPs in rectum. The basis for the difference in purinergic NMT was investigated. PDGFRα⁺ /SK3⁺ cells were closely aligned with nNOS⁺ /VIP⁺ neurons in both muscles. Gene expression of P2RY was the same in IAS and rectum (P2RY1>>P2RY2-14) while KCNN3 expression was 32% greater in rectum. The SK channel inhibitor apamin doubled contractile activity in rectum while having minimal effect in the IAS. Contractile inhibition elicited with the SK channel agonist CyPPA was five times faster in rectum than in the IAS. The P2Y1 receptor agonist MRS2365 inhibited contraction in rectum but increased contraction in the IAS. In conclusion, both the IAS and the rectum have nitrergic NMT whereas purinergic NMT is limited to rectum and VIPergic NMT to the IAS. The profile in monkey IAS more closely resembles that of humans than rodents. The lack of purinergic NMT in the IAS cannot be attributed to the absence of PDGFRα⁺ cells, P2Y1 receptors or SK3 channels. Rather, it appears to be due to poor coupling between P2Y1 receptors and SK3 channels on PDGFRα⁺ cells.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Reactive Oxygen Species Mediate the Suppression of Arterial Smooth Muscle T-type Ca2+ Channels by Angiotensin II

Vascular T-type Ca²⁺ channels (Ca_V3.1 and Ca_V3.2) play a key role in arterial tone development. This study investigated whether this conductance is a regulatory target of angiotensin II (Ang II), a vasoactive peptide that circulates and which is locally produced within the arterial wall. Patch clamp electrophysiology performed on rat cerebral arterial smooth muscle cells reveals that Ang II (100 nM) inhibited T-type currents through AT₁ receptor activation. Blocking protein kinase C failed to eliminate channel suppression, a finding consistent with unique signaling proteins enabling this response. In this regard, inhibiting NADPH oxidase (Nox) with apocynin or ML171 (Nox1 selective) abolished channel suppression highlighting a role for reactive oxygen species (ROS). In the presence of Ni²⁺ (50 µM), Ang II failed to modulate the residual T-type current, an observation consistent with this peptide targeting Ca_V3.2. Selective channel suppression by Ang II impaired the ability of Ca_V3.2 to alter spontaneous transient outward currents or vessel diameter. Proximity ligation assay confirmed Nox1 colocalization with Ca_V3.2. In closing, Ang II targets Ca_V3.2 channels via a signaling pathway involving Nox1 and the generation of ROS. This unique regulatory mechanism alters BK_Ca mediated feedback giving rise to a “constrictive” phenotype often observed with cerebrovascular disease.

Gaseous Signaling Molecules in Cardiovascular Function: From Mechanisms to Clinical Translation

Carbon monoxide (CO), hydrogen sulfide (H₂S), and nitric oxide (NO) constitute endogenous gaseous molecules produced by specific enzymes. These gases are chemically simple, but exert multiple effects and act through shared molecular targets to control both physiology and pathophysiology in the cardiovascular system (CVS). The gases act via direct and/or indirect interactions with each other in proteins such as heme-containing enzymes, the mitochondrial respiratory complex, and ion channels, among others. Studies of the major impacts of CO, H₂S, and NO on the CVS have revealed their involvement in controlling blood pressure and in reducing cardiac reperfusion injuries, although their functional roles are not limited to these conditions. In this review, the basic aspects of CO, H₂S, and NO, including their production and effects on enzymes, mitochondrial respiration and biogenesis, and ion channels are briefly addressed to provide insight into their biology with respect to the CVS. Finally, potential therapeutic applications of CO, H₂S, and NO with the CVS are addressed, based on the use of exogenous donors and different types of delivery systems.

Cav1.2 channel current block by the PKA inhibitor H-89 in rat tail artery myocytes via a PKA-independent mechanism: Electrophysiological, functional, and molecular docking studies

To characterize the role of cAMP-dependent protein kinase (PKA) in regulating vascular Ca²⁺ current through Ca_v1.2 channels [I_Ca1.2], we have documented a marked capacity of the isoquinoline H-89, widely used as a PKA inhibitor, to reduce current amplitude. We hypothesized that the I_Ca1.2 inhibitory activity of H-89 was mediated by mechanisms unrelated to PKA inhibition. To support this, an in-depth analysis of H-89 vascular effects on both I_Ca1.2 and contractility was undertaken by performing whole-cell patch-clamp recordings and functional experiments in rat tail main artery single myocytes and rings, respectively. H-89 inhibited I_Ca1.2 with a pIC₅₀ (M) value of about 5.5, even under conditions where PKA activity was either abolished by both the PKA antagonists KT5720 and protein kinase inhibitor fragment 6-22 amide or enhanced by the PKA stimulators 6-Bnz-cAMP and 8-Br-cAMP. Inhibition of I_Ca1.2 by H-89 appeared almost irreversible upon washout, was charge carrier- and voltage-dependent, and antagonised by the Ca_v1.2 channel agonist (S)-(-)-Bay K 8644. H-89 did not alter both potency and efficacy of verapamil, did not affect current kinetics or voltage-dependent activation, while shifting to the left the 50% voltage of inactivation in a concentration-dependent manner. H-89 docked at the α_1C subunit in a pocket region close to that of (S)-(-)-Bay K 8644 docking, forming a hydrogen bond with the same, key amino acid residue Tyr-1489. Finally, both high K⁺- and (S)-(-)-Bay K 8644-induced contractions of rings were fully reverted by H-89. In conclusion, these results indicate that H-89 inhibited vascular I_Ca1.2 and, consequently, the contractile function through a PKA-independent mechanism. Therefore, caution is recommended when interpreting experiments where H-89 is used to inhibit vascular smooth muscle PKA.

Mechanisms of the cyclic nucleotide cross-talk signaling network in cardiac L-type calcium channel regulation

Regulation of L-type Calcium (Ca2+) Channel (LCC) gating is critical to shaping the cardiac action potential (AP) and triggering the initiation of excitation-contraction (EC) coupling in cardiac myocytes. The cyclic nucleotide (cN) cross-talk signaling network, which encompasses the β-adrenergic and the Nitric Oxide (NO)/cGMP/Protein Kinase G (PKG) pathways and their interaction (cross-talk) through distinctively-regulated phosphodiesterase isoenzymes (PDEs), regulates LCC current via Protein Kinase A- (PKA) and PKG-mediated phosphorylation. Due to the tightly-coupled and intertwined biochemical reactions involved, it remains to be clarified how LCC gating is regulated by the signaling network from receptor to end target. In addition, the large number of EC coupling-related phosphorylation targets of PKA and PKG makes it difficult to quantify and isolate changes in L-type Ca2+ current (ICaL) responses regulated by the signaling network. We have developed a multi-scale, biophysically-detailed computational model of LCC regulation by the cN signaling network that is supported by experimental data. LCCs are modeled with functionally distinct PKA- and PKG-phosphorylation dependent gating modes. The model exhibits experimentally observed single channel characteristics, as well as whole-cell LCC currents upon activation of the cross-talk signaling network. Simulations show 1) redistribution of LCC gating modes explains changes in whole-cell current under various stimulation scenarios of the cN cross-talk network; 2) NO regulation occurs via potentiation of a gating mode characterized by prolonged closed times; and 3) due to compensatory actions of cross-talk and antagonizing functions of PKA- and PKG-mediated phosphorylation of LCCs, the effects of individual inhibitions of PDEs 2, 3, and 4 on ICaL are most pronounced at low levels of β-adrenergic stimulation. Simulations also delineate the contribution of the following two mechanisms to overall LCC regulation, which have otherwise been challenging to distinguish: 1) regulation of PKA and PKG activation via cN cross-talk (Mechanism 1); and 2) LCC interaction with activated PKA and PKG (Mechanism 2). These results provide insights into how cN signals transduced via the cN cross-talk signaling network are integrated via LCC regulation in the heart.

Smooth Muscle Ion Channels and Regulation of Vascular Tone in Resistance Arteries and Arterioles

Vascular tone of resistance arteries and arterioles determines peripheral vascular resistance, contributing to the regulation of blood pressure and blood flow to, and within the body's tissues and organs. Ion channels in the plasma membrane and endoplasmic reticulum of vascular smooth muscle cells (SMCs) in these blood vessels importantly contribute to the regulation of intracellular Ca2+ concentration, the primary determinant of SMC contractile activity and vascular tone. Ion channels provide the main source of activator Ca2+ that determines vascular tone, and strongly contribute to setting and regulating membrane potential, which, in turn, regulates the open-state-probability of voltage gated Ca2+ channels (VGCCs), the primary source of Ca2+ in resistance artery and arteriolar SMCs. Ion channel function is also modulated by vasoconstrictors and vasodilators, contributing to all aspects of the regulation of vascular tone. This review will focus on the physiology of VGCCs, voltage-gated K+ (KV) channels, large-conductance Ca2+-activated K+ (BKCa) channels, strong-inward-rectifier K+ (KIR) channels, ATP-sensitive K+ (KATP) channels, ryanodine receptors (RyRs), inositol 1,4,5-trisphosphate receptors (IP3Rs), and a variety of transient receptor potential (TRP) channels that contribute to pressure-induced myogenic tone in resistance arteries and arterioles, the modulation of the function of these ion channels by vasoconstrictors and vasodilators, their role in the functional regulation of tissue blood flow and their dysfunction in diseases such as hypertension, obesity, and diabetes. © 2017 American Physiological Society. Compr Physiol 7:485-581, 2017.

Reduced density and altered regulation of rat atrial L-type Ca2+ current in heart failure

Constitutive regulation by PKA has recently been shown to contribute to L-type Ca2+ current (ICaL) at the ventricular t-tubule in heart failure. Conversely, reduction in constitutive regulation by PKA has been proposed to underlie the downregulation of atrial ICaL in heart failure. The hypothesis that downregulation of atrial ICaL in heart failure involves reduced channel phosphorylation was examined. Anesthetized adult male Wistar rats underwent surgical coronary artery ligation (CAL, N=10) or equivalent sham-operation (Sham, N=12). Left atrial myocytes were isolated ~18 wk postsurgery and whole cell currents recorded (holding potential=-80 mV). ICaL activated by depolarizing pulses to voltages from -40 to +50 mV were normalized to cell capacitance and current density-voltage relations plotted. CAL cell capacitances were ~1.67-fold greater than Sham (P ≤ 0.0001). Maximal ICaL conductance (Gmax ) was downregulated more than 2-fold in CAL vs. Sham myocytes (P < 0.0001). Norepinephrine (1 μmol/l) increased Gmax >50% more effectively in CAL than in Sham so that differences in ICaL density were abolished. Differences between CAL and Sham Gmax were not abolished by calyculin A (100 nmol/l), suggesting that increased protein dephosphorylation did not account for ICaL downregulation. Treatment with either H-89 (10 μmol/l) or AIP (5 μmol/l) had no effect on basal currents in Sham or CAL myocytes, indicating that, in contrast to ventricular myocytes, neither PKA nor CaMKII regulated basal ICaL Expression of the L-type α1C-subunit, protein phosphatases 1 and 2A, and inhibitor-1 proteins was unchanged. In conclusion, reduction in PKA-dependent regulation did not contribute to downregulation of atrial ICaL in heart failure.NEW & NOTEWORTHY Whole cell recording of L-type Ca2+ currents in atrial myocytes from rat hearts subjected to coronary artery ligation compared with those from sham-operated controls reveals marked reduction in current density in heart failure without change in channel subunit expression and associated with altered phosphorylation independent of protein kinase A.

Ser1928 phosphorylation by PKA stimulates the L-type Ca2+ channel CaV1.2 and vasoconstriction during acute hyperglycemia and diabetes

Hypercontractility of arterial myocytes and enhanced vascular tone during diabetes are, in part, attributed to the effects of increased glucose (hyperglycemia) on L-type Ca_V1.2 channels. In murine arterial myocytes, kinase-dependent mechanisms mediate the increase in Ca_V1.2 activity in response to increased extracellular glucose. We identified a subpopulation of the Ca_V1.2 channel pore-forming subunit (α1_C) within nanometer proximity of protein kinase A (PKA) at the sarcolemma of murine and human arterial myocytes. This arrangement depended upon scaffolding of PKA by an A-kinase anchoring protein 150 (AKAP150) in mice. Glucose-mediated increases in Ca_V1.2 channel activity were associated with PKA activity, leading to α1_C phosphorylation at Ser¹⁹²⁸ Compared to arteries from low-fat diet (LFD)-fed mice and nondiabetic patients, arteries from high-fat diet (HFD)-fed mice and from diabetic patients had increased Ser¹⁹²⁸ phosphorylation and Ca_V1.2 activity. Arterial myocytes and arteries from mice lacking AKAP150 or expressing mutant AKAP150 unable to bind PKA did not exhibit increased Ser¹⁹²⁸ phosphorylation and Ca_V1.2 current density in response to increased glucose or to HFD. Consistent with a functional role for Ser¹⁹²⁸ phosphorylation, arterial myocytes and arteries from knockin mice expressing a Ca_V1.2 with Ser¹⁹²⁸ mutated to alanine (S1928A) lacked glucose-mediated increases in Ca_V1.2 activity and vasoconstriction. Furthermore, the HFD-induced increases in Ca_V1.2 current density and myogenic tone were prevented in S1928A knockin mice. These findings reveal an essential role for α1_C phosphorylation at Ser¹⁹²⁸ in stimulating Ca_V1.2 channel activity and vasoconstriction by AKAP-targeted PKA upon exposure to increased glucose and in diabetes.

Unique aspects of the developing lung circulation: structural development and regulation of vasomotor tone

This review summarizes our current knowledge on lung vasculogenesis and angiogenesis during normal lung development and the regulation of fetal and postnatal pulmonary vascular tone. In comparison to that of the adult, the pulmonary circulation of the fetus and newborn displays many unique characteristics. Moreover, altered development of pulmonary vasculature plays a more prominent role in compromised pulmonary vasoreactivity than in the adult. Clinically, a better understanding of the developmental changes in pulmonary vasculature and vasomotor tone and the mechanisms that are disrupted in disease states can lead to the development of new therapies for lung diseases characterized by impaired alveolar structure and pulmonary hypertension.

Calcium Channels in Vascular Smooth Muscle

Calcium (Ca²⁺) plays a central role in excitation, contraction, transcription, and proliferation of vascular smooth muscle cells (VSMs). Precise regulation of intracellular Ca²⁺ concentration ([Ca²⁺]_i) is crucial for proper physiological VSM function. Studies over the last several decades have revealed that VSMs express a variety of Ca²⁺-permeable channels that orchestrate a dynamic, yet finely tuned regulation of [Ca²⁺]_i. In this review, we discuss the major Ca²⁺-permeable channels expressed in VSM and their contribution to vascular physiology and pathology.

Sarcolemmal α2-adrenoceptors control protective cardiomyocyte-delimited sympathoadrenal response

Sustained cardiac adrenergic stimulation has been implicated in the development of heart failure and ventricular dysrhythmia. Conventionally, α2 adrenoceptors (α2-AR) have been assigned to a sympathetic short-loop feedback aimed at attenuating catecholamine release. We have recently revealed the expression of α2-AR in the sarcolemma of cardiomyocytes and identified the ability of α2-AR signaling to suppress spontaneous Ca²⁺ transients through nitric oxide (NO) dependent pathways. Herein, patch-clamp measurements and serine/threonine phosphatase assay revealed that, in isolated rat cardiomyocytes, activation of α2-AR suppressed L-type Ca²⁺ current (I_CaL) via stimulation of NO synthesis and protein kinase G- (PKG) dependent activation of phosphatase reactions, counteracting isoproterenol-induced β-adrenergic activation. Under stimulation with norepinephrine (NE), an agonist of β- and α-adrenoceptors, the α2-AR antagonist yohimbine substantially elevated I_CaL at NE levels >10nM. Concomitantly, yohimbine potentiated triggered intracellular Ca²⁺ dynamics and contractility of cardiac papillary muscles. Therefore, in addition to the α2-AR-mediated feedback suppression of sympathetic and adrenal catecholamine release, α2-AR in cardiomyocytes can govern a previously unrecognized local cardiomyocyte-delimited stress-reactive signaling pathway. We suggest that such aberrant α2-AR signaling may contribute to the development of cardiomyopathy under sustained sympathetic drive. Indeed, in cardiomyocytes of spontaneously hypertensive rats (SHR), an established model of cardiac hypertrophy, α2-AR signaling was dramatically reduced despite increased α2-AR mRNA levels compared to normal cardiomyocytes. Thus, targeting α2-AR signaling mechanisms in cardiomyocytes may find implications in medical strategies against maladaptive cardiac remodeling associated with chronic sympathoadrenal stimulation.

Epicardial Fat: Physiological, Pathological, and Therapeutic Implications

Epicardial fat is closely related to blood supply vessels, both anatomically and functionally, which is why any change in this adipose tissue's behavior is considered a potential risk factor for cardiovascular disease development. When proinflammatory adipokines are released from the epicardial fat, this can lead to a decrease in insulin sensitivity, low adiponectin production, and an increased proliferation of vascular smooth muscle cells. These adipokines move from one compartment to another by either transcellular passing or diffusion, thus having the ability to regulate cardiac muscle activity, a phenomenon called vasocrine regulation. The participation of these adipokines generates a state of persistent vasoconstriction, increased stiffness, and weakening of the coronary wall, consequently contributing to the formation of atherosclerotic plaques. Therefore, epicardial adipose tissue thickening should be considered a risk factor in the development of cardiovascular disease, a potential therapeutic target for cardiovascular pathology and a molecular point of contact for "endocrine-cardiology."

Rotenone-stimulated superoxide release from mitochondrial complex I acutely augments L-type Ca2+ current in A7r5 aortic smooth muscle cells

Voltage-gated L-type Ca(2+) current (ICa,L) induces contraction of arterial smooth muscle cells (ASMCs), and ICa,L is increased by H2O2 in ASMCs. Superoxide released from the mitochondrial respiratory chain (MRC) is dismutated to H2O2 We studied whether superoxide per se acutely modulates ICa,L in ASMCs using cultured A7r5 cells derived from rat aorta. Rotenone is a toxin that inhibits complex I of the MRC and increases mitochondrial superoxide release. The superoxide content of mitochondria was estimated using mitochondrial-specific MitoSOX and HPLC methods, and was shown to be increased by a brief exposure to 10 μM rotenone. ICa,L was recorded with 5 mM BAPTA in the pipette solution. Rotenone administration (10 nM to 10 μM) resulted in a greater ICa,L increase in a dose-dependent manner to a maximum of 22.1% at 10 μM for 1 min, which gradually decreased to 9% after 5 min. The rotenone-induced ICa,L increase was associated with a shift in the current-voltage relationship (I-V) to a hyperpolarizing direction. DTT administration resulted in a 17.9% increase in ICa,L without a negative shift in I-V, and rotenone produced an additional increase with a shift. H2O2 (0.3 mM) inhibited ICa,L by 13%, and additional rotenone induced an increase with a negative shift. Sustained treatment with Tempol (4-hydroxy tempo) led to a significant ICa,L increase but it inhibited the rotenone-induced increase. Staurosporine, a broad-spectrum protein kinase inhibitor, partially inhibited ICa,L and completely suppressed the rotenone-induced increase. Superoxide released from mitochondria affected protein kinases and resulted in stronger ICa,L preceding its dismutation to H2O2 The removal of nitric oxide is a likely mechanism for the increase in ICa,L.

Roles of phosphodiesterases in the regulation of the cardiac cyclic nucleotide cross-talk signaling network

The balanced signaling between the two cyclic nucleotides (cNs) cAMP and cGMP plays a critical role in regulating cardiac contractility. Their degradation is controlled by distinctly regulated phosphodiesterase isoenzymes (PDEs), which in turn are also regulated by these cNs. As a result, PDEs facilitate communication between the β-adrenergic and Nitric Oxide (NO)/cGMP/Protein Kinase G (PKG) signaling pathways, which regulate the synthesis of cAMP and cGMP respectively. The phenomena in which the cAMP and cGMP pathways influence the dynamics of each other are collectively referred to as cN cross-talk. However, the cross-talk response and the individual roles of each PDE isoenzyme in shaping this response remain to be fully characterized. We have developed a computational model of the cN cross-talk network that mechanistically integrates the β-adrenergic and NO/cGMP/PKG pathways via regulation of PDEs by both cNs. The individual model components and the integrated network model replicate experimentally observed activation-response relationships and temporal dynamics. The model predicts that, due to compensatory interactions between PDEs, NO stimulation in the presence of sub-maximal β-adrenergic stimulation results in an increase in cytosolic cAMP accumulation and corresponding increases in PKA-I and PKA-II activation; however, the potentiation is small in magnitude compared to that of NO activation of the NO/cGMP/PKG pathway. In a reciprocal manner, β-adrenergic stimulation in the presence of sub-maximal NO stimulation results in modest cGMP elevation and corresponding increase in PKG activation. In addition, we demonstrate that PDE2 hydrolyzes increasing amounts of cAMP with increasing levels of β-adrenergic stimulation, and hydrolyzes increasing amounts of cGMP with decreasing levels of NO stimulation. Finally, we show that PDE2 compensates for inhibition of PDE5 both in terms of cGMP and cAMP dynamics, leading to cGMP elevation and increased PKG activation, while maintaining whole-cell β-adrenergic responses similar to that prior to PDE5 inhibition. By defining and quantifying reactions comprising cN cross-talk, the model characterizes the cross-talk response and reveals the underlying mechanisms of PDEs in this non-linear, tightly-coupled reaction system.

Harnessing the Flow of Excitation: TRP, Voltage-Gated Na(+), and Voltage-Gated Ca(2+) Channels in Contemporary Medicine

Cellular signaling in both excitable and nonexcitable cells involves several classes of ion channels. Some of them are of minor importance, with very specialized roles in physiology, but here we concentrate on three major channel classes: TRP (transient receptor potential channels), voltage-gated sodium channels (Nav), and voltage-gated calcium channels (Cav). Here, we first propose a conceptual framework binding together all three classes of ion channels, a "flow-of-excitation model" that takes into account the inputs mediated by TRP and other similar channels, the outputs invariably provided by Cav channels, and the regenerative transmission of signals in the neural networks, for which Nav channels are responsible. We use this framework to examine the function, structure, and pharmacology of these channel classes both at cellular and also at whole-body physiological level. Building on that basis we go through the pathologies arising from the direct or indirect malfunction of the channels, utilizing ion channel defects, the channelopathies. The pharmacological interventions affecting these channels are numerous. Part of those are well-established treatments, like treatment of hypertension or some forms of epilepsy, but many other are deeply problematic due to poor drug specificity, ion channel diversity, and widespread expression of the channels in tissues other than those actually targeted.

Interaction between phosphodiesterases in the regulation of the cardiac β-adrenergic pathway

In cardiac myocytes, the second messenger cAMP is synthesized within the β-adrenergic signaling pathway upon sympathetic activation. It activates Protein Kinase A (PKA) mediated phosphorylation of multiple target proteins that are functionally critical to cardiac contractility. The dynamics of cAMP are also controlled indirectly by cGMP-mediated regulation of phosphodiesterase isoenzymes (PDEs). The nature of the interactions between cGMP and the PDEs, as well as between PDE isoforms, and how these ultimately transduce the cGMP signal to regulate cAMP remains unclear. To better understand this, we have developed mechanistically detailed models of PDEs 1-4, the primary cAMP-hydrolyzing PDEs in cardiac myocytes, and integrated them into a model of the β-adrenergic signaling pathway. The PDE models are based on experimental studies performed on purified PDEs which have demonstrated that cAMP and cGMP bind competitively to the cyclic nucleotide (cN)-binding domains of PDEs 1, 2, and 3, while PDE4 regulation occurs via PKA-mediated phosphorylation. Individual PDE models reproduce experimentally measured cAMP hydrolysis rates with dose-dependent cGMP regulation. The fully integrated model replicates experimentally observed whole-cell cAMP activation-response relationships and temporal dynamics upon varying degrees of β-adrenergic stimulation in cardiac myocytes. Simulations reveal that as a result of network interactions, reduction in the level of one PDE is partially compensated for by increased activation of others. PDE2 and PDE4 exert the strongest compensatory roles among all PDEs. In addition, PDE2 competes with other PDEs to bind and hydrolyze cAMP and is a strong regulator of PDE interactions. Finally, an increasing level of cGMP gradually out-competes cAMP for the catalytic sites of PDEs 1, 2, and 3, suppresses their cAMP hydrolysis rates, and results in amplified cAMP signaling. These results provide insights into how PDEs transduce cGMP signals to regulate cAMP and how PDE interactions affect cardiac β-adrenergic response.