Voltage-dependent Ca2+ channels in arterial smooth muscle cells

Effect of Lippia alba (Mill.) N.E. Brown Essential Oil on the Human Umbilical Artery

Lippia alba is popularly known as lemon balm, with its essential oil (EO) cited for displaying antimicrobial, sedative, and vasorelaxant effects. Yet, its action on isolated human vessels has not been described in the literature. Thus, we evaluated the vasorelaxant effect of essential oil of L. alba (EOLa) on human umbilical arteries (HUA) isolated in organ baths. HUA rings were isolated, subjected to contractions induced by potassium chloride (KCl), serotonin (5-HT), or histamine (HIST) to record the isometric tension, and then treated with EOLa (30-1000 µg/mL). The EOLa showed a more prominent inhibitory effect on the pharmacomechanical coupling contraction via HIST with an EC₅₀ value of 277.1 ± 8.5 µg/mL and maximum relaxant effect at 600 µg/mL. The addition of tetraethylammonium (TEA) or 4-aminopyridine (4-AP) in HUA preparations did not inhibit EOLa total relaxant effect at 1000 µg/mL. In the presence of gliblenclamide (GLI), the oil relaxed the HUA rings by 90.8% at maximum concentration. The EOLa was also investigated for its effects on voltage-operated calcium channels (VOCCs), where the HUA preincubation with this oil at 1000 μg/mL inhibited BaCl₂ (0.1-30 mM)-induced contractions. This study demonstrates for the first time that EOla has a vasorelaxant effect on HUA and its particular blockade of VOCCs.

Vasorelaxant effect of monoterpene carvacrol on isolated human umbilical artery

Carvacrol is the main compound of essential oils extracted primarily from Thymus and Origanum species. Its various biological activities were confirmed: antioxidant, anti-inflammatory, antibacterial, antifungal, anti-tumour, antinematodal and vasorelaxant action. Although vasodilation mediated by carvacrol was previously described, the exact mechanism of its action has not yet been established. Hence, the aim of this study was to investigate carvacrol vasoactivity on human umbilical arteries (HUA) and different pathways involved in its mechanism of action using tissue bath methodology. Carvacrol caused a significant decrease in vascular tension of 5-HT-pre-contracted umbilical arteries, with EC50 of 442.13 ± 33.8 µM (mean ± standard error of the mean - SEM). At 300 µM, carvacrol shifted downward the 5-HT concentration-response curve with statistical significance of p < 0.001 obtained for the four highest concentrations. At concentration of 1 mM, carvacrol completely abolished BaCl2-induced contraction in Ca2+-free Krebs-Ringer bicarbonate solution (p < 0.001). Isopentenyl pyrophosphate, the antagonist of TRPV3 channel, was able to decrease the efficacy of carvacrol (p < 0.001). The vasorelaxant effect of carvacrol seems to involve the blocking of L-type of Ca2+ channels on smooth muscle cells. However, the role of TRPV3 channels in carvacrol-induced vasodilation of HUA cannot be excluded either.

MARCKS mediates vascular contractility through regulating interactions between voltage-gated Ca2+ channels and PIP2

Phosphatidylinositol 4,5-bisphosphate (PIP₂) acts as substrate and unmodified ligand for Gq-protein-coupled receptor signalling in vascular smooth muscle cells (VSMCs) that is central for initiating contractility. The present work investigated how PIP₂ might perform these two potentially conflicting roles by studying the effect of myristoylated alanine-rich C kinase substrate (MARCKS), a PIP₂-binding protein, on vascular contractility in rat and mouse mesenteric arteries. Using wire myography, MANS peptide (MANS), a MARCKS inhibitor, produced robust contractions with a pharmacological profile suggesting a predominantly role for L-type (CaV1.2) voltage-gated Ca²⁺ channels (VGCC). Knockdown of MARCKS using morpholino oligonucleotides reduced contractions induced by MANS and stimulation of α₁-adrenoceptors and thromboxane receptors with methoxamine (MO) and U46619 respectively. Immunocytochemistry and proximity ligation assays demonstrated that MARCKS and CaV1.2 proteins co-localise at the plasma membrane in unstimulated tissue, and that MANS and MO reduced these interactions and induced translocation of MARCKS from the plasma membrane to the cytosol. Dot-blots revealed greater PIP₂ binding to MARCKS than CaV1.2 in unstimulated tissue, with this binding profile reversed following stimulation by MANS and MO. MANS evoked an increase in peak amplitude and shifted the activation curve to more negative membrane potentials of whole-cell voltage-gated Ca²⁺ currents, which were prevented by depleting PIP₂ levels with wortmannin. This present study indicates for the first time that MARCKS is important regulating vascular contractility and suggests that disinhibition of MARCKS by MANS or vasoconstrictors may induce contraction through releasing PIP₂ into the local environment where it increases voltage-gated Ca²⁺ channel activity.

Relaxant Effect of Monoterpene (-)-Carveol on Isolated Human Umbilical Cord Arteries and the Involvement of Ion Channels

Carveol is a monoterpene present in the structure of many plant products. It has a variety of biological activities: antioxidant, anticancer and vasorelaxation. However, studies investigating the effect of monoterpenoids on human vessels have not yet been described. Thus, the present study aimed to characterize the effect of (−)-carveol on human umbilical arteries (HUAs). HUA ring preparations were isolated and subjected to isometric tension recordings of umbilical artery smooth muscle contractions. (−)-Carveol exhibited a significant vasorelaxant effect on KCl and 5-HT-induced contractions, obtaining EC₅₀ values of 344.25 ± 8.4 and 175.82 ± 4.05 µM, respectively. The participation of calcium channels in the relaxation produced by (−)-carveol was analyzed using vessels pre-incubated with (−)-carveol (2000 µM) in a calcium-free medium, where the induction of contractions was abolished. The vasorelaxant effect of (−)-carveol on HUAs was reduced by tetraethylammonium (TEA), which increased the (−)-carveol EC₅₀ to 484.87 ± 6.55 µM. The present study revealed that (−)-carveol possesses a vasorelaxant activity in HUAs, which was dependent on the opening of calcium and potassium channels. These results pave the way for further studies involving the use of monoterpenoids for the vasodilatation of HUAs. These molecules have the potential to treat diseases such as pre-eclampsia, which is characterized by resistance in umbilical arteries.

KIR channels in the microvasculature: Regulatory properties and the lipid-hemodynamic environment

Basal tone and perfusion control is set in cerebral arteries by the sensing of pressure and flow, key hemodynamic stimuli. These forces establish a contractile foundation within arterial networks upon which local neurovascular stimuli operate. This fundamental process is intimately tied to arterial V_M and the rise in cytosolic [Ca²⁺] by the graded opening of voltage-operated Ca²⁺ channels. Arterial V_M is in turn controlled by a dynamic interaction among several resident ion channels, K_IR being one of particular significance. As the name suggests, K_IR displays strong inward rectification, retains a small outward component, potentiated by extracellular K⁺ and blocked by micromolar Ba²⁺. Cerebrovascular K_IR is unique from other K⁺ currents as it is present in both smooth muscle and endothelium yet lacking in classical regulatory modulation. Such observations have fostered the view that K_IR is nothing more than a background conductance, activated by extracellular K⁺ and which passively facilitates dilation. Recent work in cell model systems has; however, identified two membrane lipids, phosphatidylinositol 4,5-bisphosphate (PIP₂) and cholesterol, that interact with K_IR2.x, to stabilize the channel in the preferred open or silent state, respectively. Translating this unique form of regulation, recent studies have demonstrated that specific lipid-protein interactions enable unique K_IR populations to sense distinct hemodynamic stimuli and set basal tone. This review summarizes the current knowledge of vascular K_IR channels and how the lipid and hemodynamic impact their activity.

The Novel Small-molecule Annexin-A1 Mimetic, Compound 17b, Elicits Vasoprotective Actions in Streptozotocin-induced Diabetic Mice

The formyl peptide receptor (FPR) family are a group of G-protein coupled receptors that play an important role in the regulation of inflammatory processes. It is well-established that activation of FPRs can have cardioprotective properties. Recently, more stable small-molecule FPR1/2 agonists have been described, including both Compound 17b (Cmpd17b) and Compound 43 (Cmpd43). Both agonists activate a range of signals downstream of FPR1/2 activation in human-engineered FPR-expressing cells, including ERK1/2 and Akt. Importantly, Cmpd17b (but not Cmpd43) favours bias away from intracellular Ca²⁺ mobilisation in this context, which has been associated with greater cardioprotection in response to Cmpd17b over Cmpd43. However, it is unknown whether these FPR agonists impact vascular physiology and/or elicit vasoprotective effects in the context of diabetes. First, we localized FPR1 and FPR2 receptors predominantly in vascular smooth muscle cells in the aortae of male C57BL/6 mice. We then analysed the vascular effects of Cmpd17b and Cmpd43 on the aorta using wire-myography. Cmpd17b but not Cmpd43 evoked a concentration-dependent relaxation of the mouse aorta. Removal of the endothelium or blockade of endothelium-derived relaxing factors using pharmacological inhibitors had no effect on Cmpd17b-evoked relaxation, demonstrating that its direct vasodilator actions were endothelium-independent. In aortae primed with elevated K⁺ concentration, increasing concentrations of CaCl₂ evoked concentration-dependent contraction that is abolished by Cmpd17b, suggesting the involvement of the inhibition of Ca²⁺ mobilisation via voltage-gated calcium channels. Treatment with Cmpd17b for eight weeks reversed endothelial dysfunction in STZ-induced diabetic aorta through the upregulation of vasodilator prostanoids. Our data indicate that Cmpd17b is a direct endothelium-independent vasodilator, and a vasoprotective molecule in the context of diabetes.

SUMO1 modification of PKD2 channels regulates arterial contractility

PKD2 (polycystin-2, TRPP1) channels are expressed in a wide variety of cell types and can regulate functions, including cell division and contraction. Whether posttranslational modification of PKD2 modifies channel properties is unclear. Similarly uncertain are signaling mechanisms that regulate PKD2 channels in arterial smooth muscle cells (myocytes). Here, by studying inducible, cell-specific Pkd2 knockout mice, we discovered that PKD2 channels are modified by SUMO1 (small ubiquitin-like modifier 1) protein in myocytes of resistance-size arteries. At physiological intravascular pressures, PKD2 exists in approximately equal proportions as either nonsumoylated (PKD2) or triple SUMO1-modifed (SUMO-PKD2) proteins. SUMO-PKD2 recycles, whereas unmodified PKD2 is surface-resident. Intravascular pressure activates voltage-dependent Ca2+ influx that stimulates the return of internalized SUMO-PKD2 channels to the plasma membrane. In contrast, a reduction in intravascular pressure, membrane hyperpolarization, or inhibition of Ca2+ influx leads to lysosomal degradation of internalized SUMO-PKD2 protein, which reduces surface channel abundance. Through this sumoylation-dependent mechanism, intravascular pressure regulates the surface density of SUMO-PKD2-mediated Na+ currents (INa) in myocytes to control arterial contractility. We also demonstrate that intravascular pressure activates SUMO-PKD2, not PKD2, channels, as desumoylation leads to loss of INa activation in myocytes and vasodilation. In summary, this study reveals that PKD2 channels undergo posttranslational modification by SUMO1, which enables physiological regulation of their surface abundance and pressure-mediated activation in myocytes and thus control of arterial contractility.

The effect of intrauterine growth restriction on Ca2+ -activated force and contractile protein expression in the mesenteric artery of adult (6-month-old) male and female Wistar-Kyoto rats

Intrauterine growth restriction (IUGR) is known to alter vascular smooth muscle reactivity, but it is currently unknown whether these changes are driven by downstream events that lead to force development, specifically, Ca2+ -regulated activation of the contractile apparatus or a shift in contractile protein content. This study investigated the effects of IUGR on Ca2+ -activated force production, contractile protein expression, and a potential phenotypic switch in the resistance mesenteric artery of both male and female Wistar-Kyoto (WKY) rats following two different growth restriction models. Pregnant female WKY rats were randomly assigned to either a control (C; N = 9) or food restriction diet (FR; 40% of control; N = 11) at gestational day-15 or underwent a bilateral uterine vessel ligation surgery restriction (SR; N = 10) or a sham surgery control model (SC; N = 12) on day-18 of gestation. At 6-months of age, vascular responsiveness of intact mesenteric arteries was studied, before chemically permeabilization using 50 μmol/L β-escin to investigate Ca2+ -activated force. Peak responsiveness to a K+ -induced depolarization was decreased (P ≤ 0.05) due to a reduction in maximum Ca2+ -activated force (P ≤ 0.05) in both male growth restricted experimental groups. Vascular responsiveness was unchanged between female experimental groups. Segments of mesenteric artery were analyzed using Western blotting revealed IUGR reduced the relative abundance of important receptor and contractile proteins in male growth restricted rats (P ≤ 0.05), suggesting a potential phenotypic switch, whilst no changes were observed in females. Results from this study suggest that IUGR alters the mesenteric artery reactivity due to a decrease in maximum Ca2+ -activated force, and likely contributed to by a reduction in contractile protein and receptor/channel content in 6-month-old male rats, while female WKY rats appear to be protected.

Kv7 potassium channels as signal transduction intermediates in the control of microvascular tone

Potassium channels are recognized as important regulators of cellular functions in most, if not all cell types. These cellular proteins assemble to form gated pores in the plasma membrane, which serve to regulate the flow of potassium ions (K⁺ ) from the cytosol to the extracellular space. In VSMCs, the open state of potassium channels enables the efflux of K⁺ and thereby establishes a negative resting voltage across the plasma membrane that inhibits the opening of VSCCs. Under these conditions, cytosolic Ca²⁺ concentrations are relatively low and Ca²⁺ -dependent contraction is inhibited. Recent research has identified Kv7 family potassium channels as important contributors to resting membrane voltage in VSMCs, with much of the research focusing on the effects of drugs that specifically activate or block these channels to produce corresponding effects on VSMC contraction and vascular tone. Increasingly, evidence is emerging that these channels are not just good drug targets-they are also essential intermediates in vascular signal transduction, mediating vasoconstrictor or vasodilator responses to a variety of physiological stimuli. This review will summarize recent research findings that support a crucial function of Kv7 channels in both positive (vasoconstrictive) and negative (vasorelaxant) regulation of microvascular tone.

Defining the ionic mechanisms of optogenetic control of vascular tone by channelrhodopsin-2

BACKGROUND AND PURPOSE

Optogenetic control of electromechanical coupling in vascular smooth muscle cells (VSMCs) is emerging as a powerful research tool with potential applications in drug discovery and therapeutics. However, the precise ionic mechanisms involved in this control remain unclear.

EXPERIMENTAL APPROACH

Cell imaging, patch-clamp electrophysiology and muscle tension recordings were used to define these mechanisms over a wide range of light stimulations.

KEY RESULTS

Transgenic mice expressing a channelrhodopsin-2 variant [ChR2(H134R)] selectively in VSMCs were generated. Isolated VSMCs obtained from these mice demonstrated blue light-induced depolarizing whole-cell currents. Fine control of artery tone was attained by varying the intensity of the light stimulus. This arterial response was sufficient to overcome the endogenous, melanopsin-mediated, light-evoked, arterial relaxation observed in the presence of contractile agonists. Ca2+ entry through voltage-gated Ca2+ channels, and opening of plasmalemmal depolarizing channels (TMEM16A and TRPM) and intracellular IP3 receptors were involved in the ChR2(H134R)-dependent arterial response to blue light at intensities lower than ~0.1 mW·mm-2 . Light stimuli of greater intensity evoked a significant Ca2+ influx directly through ChR2(H134R) and produced marked intracellular alkalinization of VSMCs.

CONCLUSIONS AND IMPLICATIONS

We identified the range of light intensity allowing optical control of arterial tone, primarily by means of endogenous channels and without substantial alteration to intracellular pH. Within this range, mice expressing ChR2(H134R) in VSMCs are a powerful experimental model for achieving accurate and tuneable optical voltage-clamp of VSMCs and finely graded control of arterial tone, offering new approaches to the discovery of vasorelaxant drugs.

Membrane depolarization activates BK channels through ROCK-mediated β1 subunit surface trafficking to limit vasoconstriction

Membrane depolarization of smooth muscle cells (myocytes) in the small arteries that regulate regional organ blood flow leads to vasoconstriction. Membrane depolarization also activates large-conductance calcium (Ca²⁺)-activated potassium (BK) channels, which limits Ca²⁺ channel activity that promotes vasoconstriction, thus leading to vasodilation. We showed that in human and rat arterial myocytes, membrane depolarization rapidly increased the cell surface abundance of auxiliary BK β1 subunits but not that of the pore-forming BKα channels. Membrane depolarization stimulated voltage-dependent Ca²⁺ channels, leading to Ca²⁺ influx and the activation of Rho kinase (ROCK) 1 and 2. ROCK1/2-mediated activation of Rab11A promoted the delivery of β1 subunits to the plasma membrane by Rab11A-positive recycling endosomes. These additional β1 subunits associated with BKα channels already at the plasma membrane, leading to an increase in apparent Ca²⁺ sensitivity and activation of the channels in pressurized arterial myocytes and vasodilation. Thus, membrane depolarization activates BK channels through stimulation of ROCK- and Rab11A-dependent trafficking of β1 subunits to the surface of arterial myocytes.

Epigenetic regulation of L-type voltage-gated Ca2+ channels in mesenteric arteries of aging hypertensive rats

Accumulating evidence has shown that epigenetic regulation is involved in hypertension and aging. L-type voltage-gated Ca²⁺ channels (LTCCs), the dominant channels in vascular myocytes, greatly contribute to arteriole contraction and blood pressure (BP) control. We investigated the dynamic changes and epigenetic regulation of LTCC in the mesenteric arteries of aging hypertensive rats. LTCC function was evaluated by using microvascular rings and whole-cell patch-clamp in the mesenteric arteries of male Wistar-Kyoto rats and spontaneously hypertensive rats at established hypertension (3 month old) and an aging stage (16 month old), respectively. The expression of the LTCC α1C subunit was determined in the rat mesenteric microcirculation. The expression of miR-328, which targets α1C mRNA, and the DNA methylation status at the promoter region of the α1C gene (CACNA1C) were also determined. In vitro experiments were performed to assess α1C expression after transfection of the miR-328 mimic into cultured vascular smooth muscle cells (VSMCs). The results showed that hypertension superimposed with aging aggravated BP and vascular remodeling. Both LTCC function and expression were significantly increased in hypertensive arteries and downregulated with aging. miR-328 expression was inhibited in hypertension, but increased with aging. There was no significant difference in the mean DNA methylation of CACNA1C among groups, whereas methylation was enhanced in the hypertensive group at specific sites on a CpG island located upstream of the gene promoter. Overexpression of miR-328 inhibited the α1C level of cultured VSMCs within 48 h. The results of the present study indicate that the dysfunction of LTCCs may exert an epigenetic influence at both pre- and post-transcriptional levels during hypertension pathogenesis and aging progression. miR-328 negatively regulated LTCC expression in both aging and hypertension.

Aging Reduces L-Type Calcium Channel Current and the Vasodilatory Response of Small Mesenteric Arteries to Calcium Channel Blockers

Calcium channel blockers (CCBs) are widely used to treat cardiovascular disease (CVD) including hypertension. As aging is an independent risk factor for CVD, the use of CCBs increases with increasing age. Hence, this study was designed to evaluate the effect of aging on the sensitivity of small mesenteric arteries to L-type voltage-gated calcium channel (LTCC) blockers and also to investigate whether there was a concomitant change in calcium current density. Third order mesenteric arteries from male F344 rats, aged 2.5-3 months (young) and 22-26 months (old) were mounted on wire myograph to measure the tension during isometric contraction. Arteries were contracted with 100 mM KCl and were then relaxed in a cumulative concentration-response dependent manner with nifedipine (0.1 nM-1 μM), verapamil (0.1 nM-10 μM), or diltiazem (0.1 nM-10 μM). Relaxation-concentration response curves produced by cumulative concentrations of three different CCBs in arteries of old rats were shifted to the right with statistically significant IC50s. pIC50 ± s.e.m: (8.37 ± 0.06 vs. 8.04 ± 0.05, 7.40 ± 0.07 vs. 6.81 ± 0.04, and 6.58 ± 0.07 vs. 6.34 ± 0.06) in young vs. old. It was observed that the maximal contractions induced by phenylephrine and reversed by sodium nitroprusside were not different between young and old groups. However, Bay K 8644 (1 μM) increased resting tension by 23 ± 4.8% in young arteries and 4.7 ± 1.6% in old arteries. LTCC current density were also significantly lower in old arteries (-2.77 ± 0.45 pA/pF) compared to young arteries (-4.5 ± 0.40 pA/pF); with similar steady-state activation and inactivation curves. Parallel to this reduction, the expression of Cav1.2 protein was reduced by 57 ± 5% in arteries from old rats compared to those from young rats. In conclusion, our results suggest that aging reduces the response of small mesenteric arteries to the vasodilatory effect of the CCBs and this may be due to, at least in part, reduced current density of LTCC.

Local coupling of TRPC6 to ANO1/TMEM16A channels in smooth muscle cells amplifies vasoconstriction in cerebral arteries

Anoctamin-1 [ANO1, also known as transmembrane protein 16A (TMEM16A)] is a Ca(2+)-activated Cl(-) channel expressed in arterial myocytes that regulates membrane potential and contractility. Signaling mechanisms that control ANO1 activity in arterial myocytes are poorly understood. In cerebral artery myocytes, ANO1 channels are activated by local Ca(2+) signals generated by plasma membrane nonselective cation channels, but the molecular identity of these proteins is unclear. Arterial myocytes express several different nonselective cation channels, including multiple members of the transient receptor potential receptor (TRP) family. The goal of this study was to identify localized ion channels that control ANO1 currents in cerebral artery myocytes. Coimmunoprecipitation and immunofluorescence resonance energy transfer microscopy experiments indicate that ANO1 and canonical TRP 6 (TRPC6) channels are present in the same macromolecular complex and localize in close spatial proximity in the myocyte plasma membrane. In contrast, ANO1 is not near TRPC3, TRP melastatin 4, or inositol trisphosphate receptor 1 channels. Hyp9, a selective TRPC6 channel activator, stimulated Cl(-) currents in myocytes that were blocked by T16Ainh-A01, an ANO1 inhibitor, ANO1 knockdown using siRNA, and equimolar replacement of intracellular EGTA with BAPTA, a fast Ca(2+) chelator that abolishes local Ca(2+) signaling. Hyp9 constricted pressurized cerebral arteries, and this response was attenuated by T16Ainh-A01. In contrast, T16Ainh-A01 did not alter depolarization-induced (60 mM K(+)) vasoconstriction. These data indicate that TRPC6 channels generate a local intracellular Ca(2+) signal that activates nearby ANO1 channels in myocytes to stimulate vasoconstriction.

Rab25 influences functional Cav1.2 channel surface expression in arterial smooth muscle cells

Plasma membrane-localized CaV1.2 channels are the primary calcium (Ca(2+)) influx pathway in arterial smooth muscle cells (myocytes). CaV1.2 channels regulate several cellular functions, including contractility and gene expression, but the trafficking pathways that control the surface expression of these proteins are unclear. Similarly, expression and physiological functions of small Rab GTPases, proteins that control vesicular trafficking in arterial myocytes, are poorly understood. Here, we investigated Rab proteins that control functional surface abundance of CaV1.2 channels in cerebral artery myocytes. Western blotting indicated that Rab25, a GTPase previously associated with apical recycling endosomes, is expressed in cerebral artery myocytes. Immunofluorescence Förster resonance energy transfer (immunoFRET) microscopy demonstrated that Rab25 locates in close spatial proximity to CaV1.2 channels in myocytes. Rab25 knockdown using siRNA reduced CaV1.2 surface and intracellular abundance in arteries, as determined using arterial biotinylation. In contrast, CaV1.2 was not located nearby Rab11A or Rab4 and CaV1.2 protein was unaltered by Rab11A or Rab4A knockdown. Rab25 knockdown resulted in CaV1.2 degradation by a mechanism involving both lysosomal and proteasomal pathways and reduced whole cell CaV1.2 current density but did not alter voltage dependence of current activation or inactivation in isolated myocytes. Rab25 knockdown also inhibited depolarization (20-60 mM K(+)) and pressure-induced vasoconstriction (myogenic tone) in cerebral arteries. These data indicate that Rab25 is expressed in arterial myocytes where it promotes surface expression of CaV1.2 channels to control pressure- and depolarization-induced vasoconstriction.

No apparent role for T-type Ca²⁺ channels in renal autoregulation

Renal autoregulation protects glomerular capillaries against increases in renal perfusion pressure (RPP). In the mesentery, both L- and T-type calcium channels are involved in autoregulation. L-type calcium channels participate in renal autoregulation, but the role of T-type channels is not fully elucidated due to lack of selective pharmacological inhibitors. The role of T- and L-type calcium channels in the response to acute increases in RPP in T-type channel knockout mice (CaV3.1) and normo- and hypertensive rats was examined. Changes in afferent arteriolar diameter in the kidneys from wild-type and CaV3.1 knockout mice were assessed. Autoregulation of renal blood flow was examined during acute increases in RPP in normo- and hypertensive rats under pharmacological blockade of T- and L-type calcium channels using mibefradil (0.1 μM) and nifedipine (1 μM). In contrast to the results from previous pharmacological studies, genetic deletion of T-type channels CaV3.1 did not affect renal autoregulation. Pharmacological blockade of T-type channels using concentrations of mibefradil which specifically blocks T-type channels also had no effect in wild-type or knockout mice. Blockade of L-type channels significantly attenuated renal autoregulation in both strains. These findings are supported by in vivo studies where blockade of T-type channels had no effect on changes in the renal vascular resistance after acute increases in RPP in normo- and hypertensive rats. These findings show that genetic deletion of T-type channels CaV3.1 or treatment with low concentrations of mibefradil does not affect renal autoregulation. Thus, T-type calcium channels are not involved in renal autoregulation in response to acute increases in RPP.

A New Insight into the Role of Calpains in Post-mortem Meat Tenderization in Domestic Animals: A review

Tenderness is the most important meat quality trait, which is determined by intracellular environment and extracellular matrix. Particularly, specific protein degradation and protein modification can disrupt the architecture and integrity of muscle cells so that improves the meat tenderness. Endogenous proteolytic systems are responsible for modifying proteinases as well as the meat tenderization. Abundant evidence has testified that calpains (CAPNs) including calpain I (CAPN1) and calpastatin (CAST) have the closest relationship with tenderness in livestock. They are involved in a wide range of physiological processes including muscle growth and differentiation, pathological conditions and post-mortem meat aging. Whereas, Calpain3 (CAPN3) has been established as an important activating enzyme specifically expressed in livestock's skeletal muscle, but its role in domestic animals meat tenderization remains controversial. In this review, we summarize the role of CAPN1, calpain II (CAPN2) and CAST in post-mortem meat tenderization, and analyse the relationship between CAPN3 and tenderness in domestic animals. Besides, the possible mechanism affecting post-mortem meat aging and improving meat tenderization, and current possible causes responsible for divergence (whether CAPN3 contributes to animal meat tenderization or not) are inferred. Only the possible mechanism of CAPN3 in meat tenderization has been confirmed, while its exact role still needs to be studied further.

Mechanism of vasorelaxation induced by Achillea wilhelmsii in rat isolated thoracic aorta

BACKGROUND

Achillea wilhelmsii (A. wilhelmsii) is used in Iraninan folk medicine for the treatment of hypertension; also, in previous reports, the hypotensive and antihypertensive effects of this plant have been indicated. The aim of the present study is to investigate the vasorelaxant effect of the hydroalcholic extract of A. wilhelmsii and its underlying mechanisms in isolated rat aorta.

MATERIALS AND METHODS

The effect of the hydroalcholic A. wilhelmsii extract was tested on the contractile response of Wistar rat aorta induced by potassium chloride (KCl) and phenylephrine (PE) using a pressure transducer that is connected to the PowerLab.

RESULTS

The cumulative concentrations of A. wilhelmsii (0.5-8 mg/ml) induced a vasorelaxation both in endothelium-intact and endothelium-denuded aortas precontracted by high K(+) (6 × 10(-2) M) or 10(-6) M PE. A. wilhelmsii, at a concentration of 4 mg/ml, reduced Ca(2+)-induced contraction (P < 0.001 vs. control) after PE or KCl had generated a stable contraction in the Ca(2+)-free solution. Furthermore, after incubation with diltiazem, the vasorelaxant effect of A. wilhelmsii reduced in the endothelium-denuded aortas precontracted by PE or KCl (P < 0.001 vs. control). In contrast, A. wilhelmsii-induced relaxation was not affected by glibenclamide, BaCl2, ruthenium red, methylene blue, or heparin.

CONCLUSIONS

The results showed that A. wilhelmsii had a vasorelaxation effect, which was not endothelium-dependent. The relaxation was mediated by inhibition of extracellular Ca(2+) influx through voltage- and receptor-operated Ca(2+) channels (VDDCs and ROCCs) in vascular smooth muscle cells.

The voltage-dependent L-type Ca2+ (CaV1.2) channel C-terminus fragment is a bi-modal vasodilator

Voltage-dependent L-type Ca(2+) channels (CaV1.2) are the primary Ca(2+) entry pathway in vascular smooth muscle cells (myocytes). CaV1.2 channels control systemic blood pressure and organ blood flow and are pathologically altered in vascular diseases, which modifies vessel contractility. The CaV1.2 distal C-terminus is susceptible to proteolytic cleavage, which yields a truncated CaV1.2 subunit and a cleaved C-terminal fragment (CCt). Previous studies in cardiac myocytes and neurons have identified CCt as both a transcription factor and CaV1.2 channel inhibitor, with different signalling mechanisms proposed to underlie some of these effects. CCt existence and physiological functions in arterial myocytes are unclear, but important to study given the functional significance of CaV1.2 channels. Here, we show that CCt exists in myocytes of both rat and human resistance-size cerebral arteries, where it locates to both the nucleus and plasma membrane. Recombinant CCt expression in arterial myocytes inhibited CaV1.2 transcription and reduced CaV1.2 protein. CCt induced a depolarizing shift in the voltage dependence of both CaV1.2 current activation and inactivation, and reduced non-inactivating current in myocytes. Recombinant truncated CCt lacking a putative nuclear localization sequence (92CCt) did not locate to the nucleus and had no effect on arterial CaV1.2 transcription or protein. However, 92CCt shifted the voltage dependence of CaV1.2 activation and inactivation similarly to CCt. CCt and 92CCt both inhibited pressure- and depolarization-induced vasoconstriction, although CCt was a far more effective vasodilator. These data demonstrate that endogenous CCt exists and reduces both CaV1.2 channel expression and voltage sensitivity in arterial myocytes. Thus, CCt is a bi-modal vasodilator.

Transcriptional upregulation of α2δ-1 elevates arterial smooth muscle cell voltage-dependent Ca2+ channel surface expression and cerebrovascular constriction in genetic hypertension

A hallmark of hypertension is an increase in arterial myocyte voltage-dependent Ca2+ (CaV1.2) currents that induces pathological vasoconstriction. CaV1.2 channels are heteromeric complexes composed of a pore-forming CaV1.2α1 with auxiliary α2δ and β subunits. Molecular mechanisms that elevate CaV1.2 currents during hypertension and the potential contribution of CaV1.2 auxiliary subunits are unclear. Here, we investigated the pathological significance of α2δ subunits in vasoconstriction associated with hypertension. Age-dependent development of hypertension in spontaneously hypertensive rats was associated with an unequal elevation in α2δ-1 and CaV1.2α1 mRNA and protein in cerebral artery myocytes, with α2δ-1 increasing more than CaV1.2α1. Other α2δ isoforms did not emerge in hypertension. Myocytes and arteries of hypertensive spontaneously hypertensive rats displayed higher surface-localized α2δ-1 and CaV1.2α1 proteins, surface α2δ-1:CaV1.2α1 ratio, CaV1.2 current density and noninactivating current, and pressure- and depolarization-induced vasoconstriction than those of Wistar-Kyoto controls. Pregabalin, an α2δ-1 ligand, did not alter α2δ-1 or CaV1.2α1 total protein but normalized α2δ-1 and CaV1.2α1 surface expression, surface α2δ-1:CaV1.2α1, CaV1.2 current density and inactivation, and vasoconstriction in myocytes and arteries of hypertensive rats to control levels. Genetic hypertension is associated with an elevation in α2δ-1 expression that promotes surface trafficking of CaV1.2 channels in cerebral artery myocytes. This leads to an increase in CaV1.2 current-density and a reduction in current inactivation that induces vasoconstriction. Data also suggest that α2δ-1 targeting is a novel strategy that may be used to reverse pathological CaV1.2 channel trafficking to induce cerebrovascular dilation in hypertension.

Heart of the matter: coronary dysfunction in metabolic syndrome

Metabolic syndrome (MetS) is a collection of risk factors including obesity, dyslipidemia, insulin resistance/impaired glucose tolerance, and/or hypertension. The incidence of obesity has reached pandemic levels, as ~20-30% of adults in most developed countries can be classified as having MetS. This increased prevalence of MetS is critical as it is associated with a two-fold elevated risk for cardiovascular disease. Although the pathophysiology underlying this increase in disease has not been clearly defined, recent evidence indicates that alterations in the control of coronary blood flow could play an important role. The purpose of this review is to highlight current understanding of the effects of MetS on regulation of coronary blood flow and to outline the potential mechanisms involved. In particular, the role of neurohumoral modulation via sympathetic α-adrenoceptors and the renin-angiotensin-aldosterone system (RAAS) are explored. Alterations in the contribution of end-effector K(+), Ca(2+), and transient receptor potential (TRP) channels are also addressed. Finally, future perspectives and potential therapeutic targeting of the microcirculation in MetS are discussed. This article is part of a Special Issue entitled "Coronary Blood Flow".

The mechanism of vasorelaxation induced by ethanol extract of Sophora flavescens in rat aorta

AIM OF THE STUDY

Sophora flavescens (SF) is a known medicinal herb for the treatment of cardiovascular symptoms associated with arrhythmia in China. However, the pharmacological action mechanisms involved have not been well studied. The aim of the present study was to define effects of roots of SF on the vascular tension and responsible mechanisms in rat thoracic aorta.

MATERIALS AND METHODS

Ethanol extract of the roots of SF (ESF) was examined for their vascular relaxant effect in isolated phenylephrine-precontracted rat thoracic aorta.

RESULTS

ESF (0.1-100 μg/ml) induced relaxation of the phenylephrine-precontracted aortic rings in a concentration-dependent manner. Endothelium-denudation abolished the ESF-induced vasorelaxation. Pretreatment of the endothelium-intact aortic rings with l-NAME, an inhibitor of nitric oxide synthase, and ODQ, an inhibitor of soluble guanylyl cyclase (sGC), inhibited ESF-induced vasorelaxation. ESF increased cGMP levels of the aortic rings in a concentration-dependent manner and the effect was blocked by l-NAME and ODQ. Inhibition of K(+) channels with glibenclamide and tetraethylammonium, cyclooxygenase inhibition with indomethacin, and β-adrenergic and muscarinic receptors blockade had no effect on the ESF-induced vasorelaxation.

CONCLUSION

These findings suggest that ESF relaxes vascular smooth muscle via endothelium-dependent NO-sGC-cGMP signaling pathway.

Ca(V)1.2 channel N-terminal splice variants modulate functional surface expression in resistance size artery smooth muscle cells

Voltage-dependent Ca(2+) (Ca(V)1.2) channels are the primary Ca(2+) influx pathway in arterial smooth muscle cells and are essential for contractility regulation by a variety of stimuli, including intravascular pressure. Arterial smooth muscle cell Ca(V)1.2 mRNA is alternatively spliced at exon 1 (e1), generating e1b or e1c variants, with e1c exhibiting relatively smooth muscle-specific expression in the cardiovascular system. Here, we examined physiological functions of Ca(V)1.2e1 variants and tested the hypothesis that targeting Ca(V)1.2e1 modulates resistance size cerebral artery contractility. Custom antibodies that selectively recognize Ca(V)1.2 channel proteins containing sequences encoded by either e1b (Ca(V)1.2e1b) or e1c (Ca(V)1.2e1c) both detected Ca(V)1.2 in rat and human cerebral arteries. shRNA targeting e1b or e1c reduced expression of that Ca(V)1.2 variant, induced compensatory up-regulation of the other variant, decreased total Ca(V)1.2, and reduced intravascular pressure- and depolarization-induced vasoconstriction. Ca(V)1.2e1b and Ca(V)1.2e1c knockdown reduced whole cell Ca(V)1.2 currents, with Ca(V)1.2e1c knockdown most effectively reducing total Ca(V)1.2 and inducing the largest vasodilation. Knockdown of α(2)δ-1, a Ca(V)1.2 auxiliary subunit, reduced surface expression of both Ca(V)1.2e1 variants, inhibiting Ca(V)1.2e1c more than Ca(V)1.2e1b. e1b or e1c overexpression reduced Ca(V)1.2 surface expression and whole cell currents, leading to vasodilation, with e1c overexpression inducing the largest effect. In summary, data indicate that arterial smooth muscle cells express Ca(V)1.2 channels containing e1b or e1c-encoded N termini that contribute to Ca(V)1.2 surface expression, α(2)δ-1 preferentially traffics the Ca(V)1.2e1c variant to the plasma membrane, and targeting of Ca(V)1.2e1 message or the Ca(V)1.2 channel proximal N terminus induces vasodilation.

Smooth muscle cell alpha2delta-1 subunits are essential for vasoregulation by CaV1.2 channels

RATIONALE

Voltage-dependent L-type (Ca(V)1.2) Ca(2+) channels are a heteromeric complex formed from pore-forming alpha(1) and auxiliary alpha(2)delta and beta subunits. Ca(V)1.2 channels are the principal Ca(2+) influx pathway in arterial myocytes and regulate multiple physiological functions, including contraction. The macromolecular composition of arterial myocyte Ca(V)1.2 channels remains poorly understood, with no studies having examined the molecular identity or physiological functions of alpha(2)delta subunits.

OBJECTIVE

We investigated the functional significance of alpha(2)delta subunits in myocytes of resistance-size (100 to 200 mum diameter) cerebral arteries.

METHODS AND RESULTS

alpha(2)delta-1 was the only alpha(2)delta isoform expressed in cerebral artery myocytes. Pregabalin, an alpha(2)delta-1/-2 ligand, and an alpha(2)delta-1 antibody, inhibited Ca(V)1.2 currents in isolated myocytes. Acute pregabalin application reversibly dilated pressurized arteries. Using a novel application of surface biotinylation, data indicated that >95% of Ca(V)1.2 alpha(1) and alpha(2)delta-1 subunits were present in the arterial myocyte plasma membrane. Alpha(2)delta-1 knockdown using short hairpin RNA reduced plasma membrane-localized Ca(V)1.2 alpha(1) subunits, caused a corresponding elevation in cytosolic Ca(V)1.2 alpha(1) subunits, decreased intracellular Ca(2+) concentration, inhibited pressure-induced vasoconstriction ("myogenic tone"), and attenuated pregabalin-induced vasodilation. Prolonged (24-hour) pregabalin exposure did not alter total alpha(2)delta-1 or Ca(V)1.2 alpha(1) proteins but decreased plasma membrane expression of each subunit, which reduced myogenic tone.

CONCLUSIONS

alpha(2)delta-1 is essential for plasma membrane expression of arterial myocyte Ca(V)1.2 alpha(1) subunits. alpha(2)delta-1 targeting can block Ca(V)1.2 channels directly and inhibit surface expression of Ca(V)1.2 alpha(1) subunits, leading to vasodilation. These data identify alpha(2)delta-1 as a novel molecular target in arterial myocytes, the manipulation of which regulates contractility.

Alternative splicing of Cav1.2 channel exons in smooth muscle cells of resistance-size arteries generates currents with unique electrophysiological properties

Voltage-dependent calcium (Ca(2+), Ca(V)1.2) channels are the primary Ca(2+) entry pathway in smooth muscle cells of resistance-size (myogenic) arteries, but their molecular identity remains unclear. Here we identified and quantified Ca(V)1.2 alpha(1)-subunit splice variation in myocytes of rat resistance-size (100-200 microm diameter) cerebral arteries. Full-length clones containing either exon 1b or the recently identified exon 1c exhibited additional primary splice variation at exons 9*, 21/22, 31/32, and +/- 33. Real-time PCR confirmed the findings from full-length clones and indicated that the major Ca(V)1.2 variant contained exons 1c, 8, 21, and 32+33, with approximately 57% containing 9*. Exon 9* was more prevalent in clones containing 1c (72%) than in those containing 1b (33%), suggesting exon-selective combinatorial splicing. To examine the functional significance of this splicing profile, membrane currents produced by each of the four exon 1b/c/ +/- 9* variants were characterized following transfection in HEK293 cells. Exon 1c and 9* caused similar hyperpolarizing shifts in both current-voltage relationships and voltage-dependent activation of currents. Furthermore, exon 9* induced a hyperpolarizing shift only in the voltage-dependent activation of channels containing exon 1b, but not in those containing exon 1c. In contrast, exon 1b, 1c, or +9* did not alter voltage-dependent inactivation. In summary, we have identified the Ca(V)1.2 alpha(1)-subunit splice variant population that is expressed in myocytes of resistance-size arteries and the unique electrophysiological properties of recombinant channels formed by exon 1 and 9* variation. The predominance of exon 1c and 9* in smooth muscle cell Ca(V)1.2 channels causes a hyperpolarizing shift in the voltage sensitivity of currents toward the physiological arterial voltage range.

Elevations of intracellular calcium reflect normal voltage-dependent behavior, and not constitutive activity, of voltage-dependent calcium channels in gastrointestinal and vascular smooth muscle

In smooth muscle, the gating of dihydropyridine-sensitive Ca²⁺ channels may either be stochastic and voltage dependent or coordinated among channels and constitutively active. Each form of gating has been proposed to be largely responsible for Ca²⁺ influx and determining the bulk average cytoplasmic Ca²⁺ concentration. Here, the contribution of voltage-dependent and constitutively active channel behavior to Ca²⁺ signaling has been studied in voltage-clamped single vascular and gastrointestinal smooth muscle cells using wide-field epifluorescence with near simultaneous total internal reflection fluorescence microscopy. Depolarization (−70 to +10 mV) activated a dihydropyridine-sensitive voltage-dependent Ca²⁺ current (I_Ca) and evoked a rise in [Ca²⁺] in each of the subplasma membrane space and bulk cytoplasm. In various regions of the bulk cytoplasm the [Ca²⁺] increase ([Ca²⁺]_c) was approximately uniform, whereas that of the subplasma membrane space ([Ca²⁺]_PM) had a wide range of amplitudes and time courses. The variations that occurred in the subplasma membrane space presumably reflected an uneven distribution of active Ca²⁺ channels (clusters) across the sarcolemma, and their activation appeared consistent with normal voltage-dependent behavior. Indeed, in the present study, dihydropyridine-sensitive Ca²⁺ channels were not normally constitutively active. The repetitive localized [Ca²⁺]_PM rises (“persistent Ca²⁺ sparklets”) that characterize constitutively active channels were observed rarely (2 of 306 cells). Neither did dihydropyridine-sensitive constitutively active Ca²⁺ channels regulate the bulk average [Ca²⁺]_c. A dihydropyridine blocker of Ca²⁺ channels, nimodipine, which blocked I_Ca and accompanying [Ca²⁺]_c rise, reduced neither the resting bulk average [Ca²⁺]_c (at −70 mV) nor the rise in [Ca²⁺]_c, which accompanied an increased electrochemical driving force on the ion by hyperpolarization (−130 mV). Activation of protein kinase C with indolactam-V did not induce constitutive channel activity. Thus, although voltage-dependent Ca²⁺ channels appear clustered in certain regions of the plasma membrane, constitutive activity is unlikely to play a major role in [Ca²⁺]_c regulation. The stochastic, voltage-dependent activity of the channel provides the major mechanism to generate rises in [Ca²⁺].

Isolation and culture of human umbilical artery smooth muscle cells expressing functional calcium channels

The human umbilical cord is a biological sample that can be easily obtained just after birth. A methodology was developed to perform cultures of human umbilical artery smooth muscle cells (HUASMC) expressing contractile proteins and functional ionic channels. To avoid fibroblast and endothelial cell contamination, we mechanically separated the tunica media, which only contains HUASMC and matrix proteins. To isolate the cells, collagenase V and elastase were used as hydrolyzing enzymes. The isolated cells were plated in collagen-coated dishes to obtain cultures of HUASMC. The cells obtained after different passages (1 to 6) exhibit the characteristic vascular smooth cell morphology and express smooth muscle alpha-2 actin, myosin heavy chain SM1, and alpha subunits of L- and T-type calcium channels (Cav 1.2, Cav 1.2, and Cav 3.2). Electrophysiology recordings for L- and T-type calcium channels were made, indicating that these channels are functional in the cultured cells. In conclusion, the procedure developed allows obtaining cultures of HUASMC expressing contractile proteins and also functional ionic channels. These cells could be used to study cellular and molecular aspects about the regulation of the vascular function.

Inhibition of L-type calcium channels in arteriolar smooth muscle cells is involved in the pathogenesis of vascular hyporeactivity in severe shock

The objective was to investigate the changes in the function of L-type calcium (L-Ca2+) channels of arteriolar smooth muscle cells (ASMCs) in the genesis of vascular hyporeactivity during severe shock. A hemorrhagic shock (HS) model was reproduced in rats, and the responsiveness of arterioles in the cremaster muscle to norepinephrine (NE) was measured. The inward currents of L-Ca2+ channel and intracellular concentration of Ca2+ ([Ca2+]i) level in isolated ASMCs were measured using patch clamp and fluorescent probe techniques. The arteriolar vasoreactivity was significantly reduced with a 12.5-fold increase of NE threshold level 2 h post-HS. Meanwhile, the inward currents through L-Ca2+ channels of ASMCs were significantly decreased at different holding potentials, and the maximal inward current was only 26.7% of control value in the shock group. The increased intracellular concentration of Ca2+ level of ASMCs stimulated by NE was reduced to 32.0% of control value 2 h post-HS. Administration of the L-Ca2+ channel stimulator, Bay K8644, partially restored the NE threshold level and transiently increased the mean arterial pressure during HS, lending further support to the importance of ASMC L-Ca2+ channel inhibition in the genesis of low vasoreactivity in vivo during severe shock. Our results suggest that stimulation of L-Ca2+ channels of ASMCs might be a potential therapeutic approach for treatment of refractory hypotension in severe shock.

Ca2+ channel inactivation in small mesenteric arteries of WKY and SHR

BACKGROUND

This study was designed to test the hypothesis that differences exist in the inactivation properties of voltage-gated Ca(2+) channels (Ca(V)) in hypertensive arterial smooth muscle cells (ASMCs), and that these differences contribute to enhanced Ca(V) activity.

METHODS

The properties of Ca(V) were studied in freshly isolated myocytes from small mesenteric arteries (SMAs) of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs) using whole-cell patch-clamp methods.

RESULTS

Peak currents (I(Ca)) were larger in SHR with either 2 mmol/l Ca(2+) or Ba(2+) as the charge carrier. In WKY and SHR, the peak current was larger with Ba(2+) than with Ca(2+) with no difference in their ratio. The voltage dependence of Ca(V) activation was shifted to the left in SHR as compared to WKY for Ca(2+) but not for Ba(2+), while availability was not different. The time course of inactivation of current could be represented by two time constants, both of which were larger in SHR than in WKY and also larger for Ba(2+) than for Ca(2+), with a greater fraction of inactivation being associated with the process slower in SHR and with Ba(2+). The time courses of availability, inactivation, and recovery from inactivation were faster in SHR than in WKY in the case of Ca(2+), but there was no difference in the case of Ba(2+).

CONCLUSIONS

These results demonstrate that there are differences between WKY and SHR in the inactivation properties of SMA Ca(V), and that these differences could contribute to larger steady-state currents. The differences cannot be explained merely by the presence of a larger number of identical Ca(V) complexes, and it appears likely that differences in intrinsic compositions, primary structures, and/or regulation are involved.

The non-excitable smooth muscle: calcium signaling and phenotypic switching during vascular disease

Calcium (Ca(2+)) is a highly versatile second messenger that controls vascular smooth muscle cell (VSMC) contraction, proliferation, and migration. By means of Ca(2+) permeable channels, Ca(2+) pumps and channels conducting other ions such as potassium and chloride, VSMC keep intracellular Ca(2+) levels under tight control. In healthy quiescent contractile VSMC, two important components of the Ca(2+) signaling pathways that regulate VSMC contraction are the plasma membrane voltage-operated Ca(2+) channel of the high voltage-activated type (L-type) and the sarcoplasmic reticulum Ca(2+) release channel, Ryanodine Receptor (RyR). Injury to the vessel wall is accompanied by VSMC phenotype switch from a contractile quiescent to a proliferative motile phenotype (synthetic phenotype) and by alteration of many components of VSMC Ca(2+) signaling pathways. Specifically, this switch that culminates in a VSMC phenotype reminiscent of a non-excitable cell is characterized by loss of L-type channels expression and increased expression of the low voltage-activated (T-type) Ca(2+) channels and the canonical transient receptor potential (TRPC) channels. The expression levels of intracellular Ca(2+) release channels, pumps and Ca(2+)-activated proteins are also altered: the proliferative VSMC lose the RyR3 and the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase isoform 2a pump and reciprocally regulate isoforms of the ca(2+)/calmodulin-dependent protein kinase II. This review focuses on the changes in expression of Ca(2+) signaling proteins associated with VSMC proliferation both in vitro and in vivo. The physiological implications of the altered expression of these Ca(2+) signaling molecules, their contribution to VSMC dysfunction during vascular disease and their potential as targets for drug therapy will be discussed.

A novel Ca(V)1.2 N terminus expressed in smooth muscle cells of resistance size arteries modifies channel regulation by auxiliary subunits

Voltage-dependent L-type Ca(2+) (Ca(V)1.2) channels are the principal Ca(2+) entry pathway in arterial myocytes. Ca(V)1.2 channels regulate multiple vascular functions and are implicated in the pathogenesis of human disease, including hypertension. However, the molecular identity of Ca(V)1.2 channels expressed in myocytes of myogenic arteries that regulate vascular pressure and blood flow is unknown. Here, we cloned Ca(V)1.2 subunits from resistance size cerebral arteries and demonstrate that myocytes contain a novel, cysteine rich N terminus that is derived from exon 1 (termed "exon 1c"), which is located within CACNA1C, the Ca(V)1.2 gene. Quantitative PCR revealed that exon 1c was predominant in arterial myocytes, but rare in cardiac myocytes, where exon 1a prevailed. When co-expressed with alpha(2)delta subunits, Ca(V)1.2 channels containing the novel exon 1c-derived N terminus exhibited: 1) smaller whole cell current density, 2) more negative voltages of half activation (V(1/2,act)) and half-inactivation (V(1/2,inact)), and 3) reduced plasma membrane insertion, when compared with channels containing exon 1b. beta(1b) and beta(2a) subunits caused negative shifts in the V(1/2,act) and V(1/2,inact) of exon 1b-containing Ca(V)1.2alpha(1)/alpha(2)delta currents that were larger than those in exon 1c-containing Ca(V)1.2alpha(1)/alpha(2)delta currents. In contrast, beta(3) similarly shifted V(1/2,act) and V(1/2,inact) of currents generated by exon 1b- and exon 1c-containing channels. beta subunits isoform-dependent differences in current inactivation rates were also detected between N-terminal variants. Data indicate that through novel alternative splicing at exon 1, the Ca(V)1.2 N terminus modifies regulation by auxiliary subunits. The novel exon 1c should generate distinct voltage-dependent Ca(2+) entry in arterial myocytes, resulting in tissue-specific Ca(2+) signaling.

Cellular and molecular mechanisms regulating vascular tone. Part 1: basic mechanisms controlling cytosolic Ca2+ concentration and the Ca2+-dependent regulation of vascular tone

General anesthetics cause hemodynamic instability and alter blood flow to various organs. There is mounting evidence that most general anesthetics, at clinical concentrations, influence a wide variety of cellular and molecular mechanisms regulating the contractile state of vascular smooth muscle cells (i.e., vascular tone). In addition, in current anesthetic practice, various types of vasoactive agents are often used to control vascular reactivity and to sustain tissue blood flow in high-risk surgical patients with impaired vital organ function and/or hemodynamic instability. Understanding the physiological mechanisms involved in the regulation of vascular tone thus would be beneficial for anesthesiologists. This review, in two parts, provides an overview of current knowledge about the cellular and molecular mechanisms regulating vascular tone-i.e., targets for general anesthetics, as well as for vasoactive drugs that are used in intraoperative circulatory management. This first part of the two-part review focuses on basic mechanisms regulating cytosolic Ca2+ concentration and the Ca2+-dependent regulation of vascular tone.

Signaling pathway underlying stimulation of L-type Ca2+ channels in rabbit portal vein myocytes by recombinant Gbetagamma subunits

In previous studies, we (Callaghan B, Koh SD, and Keef KD, Circ Res 94: 626-633, 2004) have shown that voltage-dependent L-type Ca(2+) channels (Cav) in portal vein myocytes are enhanced when muscarinic M2 receptors are activated with ACh. Current stimulation was coupled to the G protein subunit Gbetagamma along with the downstream mediators phosphatidylinositol-3-kinase (PI3K), protein kinase C (PKC), and c-Src. The present study was designed to determine whether the same second messenger pathway could be identified when exogenous recombinant Gbetagamma subunits are introduced into cells. Smooth muscle myocytes were freshly isolated from rabbit portal vein, and Cav currents were recorded by using the patch-clamp technique. Dialysis of cells with recombinant Gbetagamma (50 nM) significantly increased Cav currents (141%). Nifedipine (1 microM) reduced both control and stimulated currents by approximately 90%. The enhancement of current by Gbetagamma was equivalent to that produced by ACh (142%), whereas the PKC activator phorbol 12,13-dibutyrate (PdBu) gave rise to greater current stimulation (192%). Current stimulation with Gbetagamma, ACh, and PdBu were not associated with changes in the voltage dependence of activation or inactivation. The PI3K inhibitor LY-294002 (20 microM) reduced peak currents by 32% in cells dialyzed with Gbetagamma, whereas the inactive analog LY-303511 resulted in a small but significant reduction in current (12%). The c-Src inhibitor PP2 (1 microM) also significantly reduced currents (34%), whereas the inactive analog PP3 was without effect. These data provide further evidence for the hypothesis that Gbetagamma leads to stimulation of Cav currents in rabbit portal vein myocytes via a signaling pathway that includes PI3K, PKC, and c-Src.

Multiple actions of halothane on contractile response to noradrenaline in isolated mesenteric resistance arteries

Halothane, a volatile anaesthetic, produces systemic hypotension and significantly alters organ blood flow. Isometric force was recorded in isolated rat small mesenteric arteries to investigate its action on contractile response to noradrenaline, the sympathetic neurotransmitter. Halothane (1-5%) enhanced contractile response to noradrenaline in the endothelium-intact arteries, but had little influence in the endothelium-denuded arteries. However, halothane consistently inhibited the noradrenaline response in the endothelium-denuded arteries pretreated with ryanodine (10 microM). The enhancement of the contractile response to noradrenaline in the endothelium-intact arteries was unaffected by treatment with N(G)-nitro L-arginine, tetraethylammonium, apamin, charybdotoxin, indomethacin, diclofenac, nordihydroguaiaretic acid, BQ-123, BQ-788, losartan, ketanserin, or superoxide dismutase. Halothane prolonged vasorelaxation after washout of noradrenaline in the endothelium-denuded arteries. Both ryanodine and vanadate (0.1-0.3 mM), a putative inhibitor of the plasma membrane Ca2+-ATPase, also prolonged the vasorelaxation. Halothane still prolonged the vasorelaxation in the ryanodine-treated arteries, but not in the vanadate-treated arteries. Halothane decreased the pD2 value for the pCa-force relation in the beta-escin-permeabilised, endothelium-denuded arteries. Halothane appears to influence contractile response to noradrenaline through multiple actions including endothelium-dependent enhancing, endothelium-independent enhancing, and endothelium-independent inhibitory actions. Nitric oxide, endothelium-derived hyperpolarising factor, cyclooxygenase products, lipoxygenase products, endothelin-1, angiotensin-II, serotonin, and superoxide anions are not involved in the endothelium-dependent enhancement. The endothelium-independent enhancement is presumably due to its ability to stimulate Ca2+ release from the ryanodine-sensitive intracellular stores, while the endothelium-independent inhibition is due, at least in part, to depressed Ca2+-activation of contractile proteins. Halothane may inhibit the plasma membrane Ca2+-ATPase of vascular smooth muscle cells.

Muscarinic M2 Receptor Stimulation of Cav1.2b Requires Phosphatidylinositol 3-Kinase, Protein Kinase C, and c-Src

This study investigated regulation of L-type calcium channels (Cav1.2b) by acetylcholine (ACh) in rabbit portal vein myocytes. Whole-cell currents were recorded using 5 mmol/L barium as charge carrier. ACh (10 μmol/L) increased peak currents by 40%. This effect was not reversed by the selective muscarinic M3 receptor antagonist 4-DAMP (100 nmol/L) but was blocked by the M2 receptor antagonist methoctramine (5 μmol/L). The classical and novel protein kinase C (PKC) antagonist calphostin C (50 nmol/L) abolished ACh responses, whereas the classical PKC antagonist Gö6976 (200 nmol/L) had no effect. ACh responses were also abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (20 μmol/L), by the c-Src inhibitor PP2 (10 μmol/L) (but not the inactive analogue PP3), and by dialyzing cells with an antibody to the G-protein subunit Gβγ. Cells dialyzed with c-Src had significantly greater currents than control cells. Current enhancement persisted in the presence of LY294002, suggesting that c-Src is downstream of PI3K. Phorbol 12,13-dibutyrate (PDBu, 0.1 μmol/L) increased currents by 74%. This effect was abolished by calphostin C and reduced by Gö6976. The PDBu response was also reduced by PP2, and the PP2-insensitive component was blocked by Gö6976. In summary, these data suggest that ACh enhances Cav1.2b currents via M2 receptors that couple sequentially to Gβγ, PI3K, a novel PKC, and c-Src. PDBu stimulates the novel PKC/c-Src pathway along with a second pathway that is independent of c-Src and involves a classical PKC.

Locally released norepinephrine in the oxygen-dependent regulation of vascular tone of human umbilical vein

In a previous study, human umbilical vein preparations constricted at PO(2) values above the physiologic intrauterine PO(2) range and dilated at hypoxia. Denudation of the endothelium reversed the hypoxic vasodilatation only, suggesting the release of a nonendothelial vasoconstrictor. We therefore hypothesized that norepinephrine from adrenergic nerve terminals could be responsible for the observed constricting effects. We measured intracellular membrane potential and isometric tension of human umbilical vein strips with and without functional adrenergic denervation by 6-OH-dopamine during variation of PO(2). With PO(2) increasing from 5 to 104 mm Hg, intact preparations depolarized of from -58.6 +/- 1.1 mV (SEM) to -53.3 +/- 1.0 mV (p < 0.001) and isometric tension increased from 0.673 +/- 0.037 g to 0.825 +/- 0.044 g (p < 0.02). Intact preparations pretreated with 6-OH-dopamine depolarized from -58.0 +/- 0.5 mV to -55.8 +/- 0.6 mV (p < 0.01), and isometric tension increased from 0.598 +/- 0.040 g to 0.661 +/- 0.018 g (p < 0.02). At Po(2) values above the physiologic intrauterine umbilical venous Po(2) range, membrane potential and isometric tension were significantly lower in preparations with 6-OH-dopamine pretreatment compared with matched controls (p < 0.05). Denudation of the endothelium reversed the hypoxic hyperpolarization and vasodilatation observed in intact preparations. However, membrane potential and isometric tension were not different between endothelium-denuded preparations with and without 6-OH-dopamine pretreatment. We conclude that locally released norepinephrine contributes to the depolarization and vasoconstriction of the human umbilical vein at hyperoxia but does not antagonize the endothelium-dependent vasodilation at hypoxia.

Diverse effects of monensin on capacitative Ca2+ entry and release of stored Ca2+ in vascular smooth muscle cells

The effects of monensin, an activator of Na(+)/H(+) exchanger (NHE), on capacitative Ca(2+) entry (CCE) were investigated using A7r5 cells. Capacitative Ca(2+) entry was induced by elevation of extracellular Ca(2+) concentrations of A7r5 cells in which stored Ca(2+) had been depleted by previous administration of thapsigargin. Capacitative Ca(2+) entry was abolished by pretreatment of the cells with SKF-96365 (1-[beta-(3-[4-methoxyphenyl]propoxy)-4-methoxyphenethyl]-1H-imidazole hydrochloride) but was not affected by pretreatment with verapamil. Monensin significantly increased capacitative Ca(2+) entry. On the other hand, 5-hydroxytryptamine-induced inositol monophosphate accumulation and subsequent intracellular Ca(2+) release from its stores were significantly inhibited by monensin, while thapsigargin-induced Ca(2+) release was not affected by monensin. These results suggest that monensin has diverse actions on capacitative Ca(2+) entry and agonist-induced release of stored Ca(2+) in vascular smooth muscle cells.

[Analyses of Ca-related ion channel currents and their involvement in Ca mobilization in smooth muscle and endothelial cells]

Changes in intracellular Ca concentration ([Ca2+]i) play dominant roles in the regulation of ion channel activity. Thus, analyses of Ca-related ion channels, whose activation is responsible for and/or dependent on the changes in [Ca2+]i, are important to understand the physiological and pharmacological characteristics of smooth muscle cells (SMCs) and endothelial cells (ECs). We have clarified that, in SMCs, Ca mobilization by membrane depolarization and bioactive substances affects the activity of Ca-activated K (IK-Ca) and Cl channel currents. On the other hand, by measuring IK-Ca as an indicator of Ca mobilization, we found that palmitoylcarnitine (PC), a lipid released under ischemic conditions, mobilizes Ca in ECs via stimulation of endothelial differential gene (Edg) receptors. Moreover, sphingosine-1-phosphate, which is a lipid mediator and has a similar structure to PC, elevated [Ca2+]i in ECs via the activation of cation channels through Edg1 receptors. A myo-endothelial interaction is another regulatory factor of Ca mobilization in ECs as well as in SMCs. Nifedipine and levcromakalim, which have no effects on ion channels in ECs themselves, changed the membrane potential of ECs via a myo-endothelial pathway. These integral analyses provide better understanding of the functional roles of Ca-related ion channels and their involvement in Ca mobilization in SMCs and ECs.

Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

We have previously identified alpha-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that alpha-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)-induced contraction of rat aortic rings. Addition of 1 microM alpha-defensin increased the half-maximal effective concentration (EC(50)) of PE on denuded aortic rings from 32 to 630 nM. The effect of alpha-defensin was dose dependent and saturable, with a half-maximal effect at 1 microM. alpha-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 microM alpha-defensin inhibited the PE-mediated Ca(++) mobilization in SMCs by more than 80%. The inhibitory effect of alpha-defensin on contraction of aortic rings and Ca(++) mobilization was completely abolished by anti-low-density lipoprotein receptor-related protein/alpha(2-)macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). alpha-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. alpha-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, alpha and beta. RAP and anti-LRP antibodies inhibited the binding and internalization of alpha-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of alpha-defensin to LRP expressed in SMCs leads to its internalization; internalized alpha-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca(++) mobilization and SMC contraction in response to PE.

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

High voltage-activated Ca(2+) channels of the Ca(V)1.2 class (L-type) are crucial for excitation-contraction coupling in both cardiac and smooth muscle. These channels are regulated by a variety of second messenger pathways that ultimately serve to modulate the level of contractile force in the tissue. The specific focus of this review is on the most recent advances in our understanding of how cardiac Ca(V)1.2a and smooth muscle Ca(V)1.2b channels are regulated by different kinases, including cGMP-dependent protein kinase, cAMP-dependent protein kinase, and protein kinase C. This review also discusses recent evidence regarding the regulation of these channels by protein tyrosine kinase, calmodulin-dependent kinase, purified G protein subunits, and identification of possible amino acid residues of the channel responsible for kinase regulation.

The pathobiology of pulmonary hypertension. Smooth muscle cells and ion channels

Chronic hypoxic pulmonary arterial hypertension, APAH, and PPAH are characterized by vasoconstriction and vascular remodeling and are associated with decreased Kv currents in PA smooth muscle cells. Although Kv2.1 is less well studied, it seems that Kv1.5 is particularly important in the pulmonary circulation in animals and humans because it has been implicated in physiologic phenomena (HPV) and all of the aforementioned pulmonary hypertensive disorders. This occurrence is perhaps because of the fact that it controls Em in the PA smooth muscle cells and it has a short turnover half time. It is also certain that the pathogenesis of PPAH is multifactorial and not a result of a single abnormality. The recently discovered "PPAH gene" in chromosome 2q in patients with familial PPAH (6%-12% of patients) does not seem to encode for any Kv channels. Kv1.5 abnormalities, however, are likely to be a strong predisposing factor that, in association with others such as endothelial dysfunction, [figure: see text] anorexigen use, or viral infections, will initiate a process that eventually leads to PPAH. The selective Kv1.5 down-regulation leaves wide open the door to replacement gene therapy in pulmonary hypertension research.

Nifedipine blocks Ca2+ store refilling through a pathway not involving L-type Ca2+ channels in rabbit arteriolar smooth muscle

This study assessed the contribution of L-type Ca2+ channels and other Ca2+ entry pathways to Ca2+ store refilling in choroidal arteriolar smooth muscle. Voltage-clamp recordings were made from enzymatically isolated choroidal microvascular smooth muscle cells and from cells within vessel fragments (containing < 10 cells) using the whole-cell perforated patch-clamp technique. Cell Ca2+ was estimated by fura-2 microfluorimetry. After Ca2+ store depletion with caffeine (10 mM), refilling was slower in cells held at -20 mV compared to -80 mV (refilling half-time was 38 +/- 10 and 20 +/- 6 s, respectively). To attempt faster refilling via L-type Ca2+ channels, depolarising steps from -60 to -20 mV were applied during a 30 s refilling period following caffeine depletion. Each step activated L-type Ca2+ currents and [Ca2+]i transients, but failed to accelerate refilling. At -80 mV and in 20 mM TEA, prolonged caffeine exposure produced a transient Ca2+-activated Cl- current (I(Cl)(Ca)) followed by a smaller sustained current. The sustained current was resistant to anthracene-9-carboxylic acid (1 mM; an I(Cl)(Ca) blocker) and to BAPTA AM, but was abolished by 1 microM nifedipine. This nifedipine-sensitive current reversed at +29 +/- 2 mV, which shifted to +7 +/- 5 mV in Ca2+-free solution. Cyclopiazonic acid (20 microM; an inhibitor of sarcoplasmic reticulum Ca2+-ATPase) also activated the nifedipine-sensitive sustained current. At -80 mV, a 5 s caffeine exposure emptied Ca2+ stores and elicited a transient I(Cl)(Ca). After 80 s refilling, another caffeine challenge produced a similar inward current. Nifedipine (1 microM) during refilling reduced the caffeine-activated I(Cl)(Ca) by 38 +/- 5 %. The effect was concentration dependent (1-3000 nM, EC50 64 nM). In Ca2+-free solution, store refilling was similarly depressed (by 46 +/- 6 %). Endothelin-1 (10 nM) applied at -80 mV increased [Ca2+]i, which subsided to a sustained 198 +/- 28 nM above basal. Cell Ca2+ was then lowered by 1 microM nifedipine (to 135 +/- 22 nM), which reversed on washout. These results show that L-type Ca2+ channels fail to contribute to Ca2+ store refilling in choroidal arteriolar smooth muscle. Instead, they refill via a novel non-selective store-operated cation conductance that is blocked by nifedipine.

Chronic nicotine alters NO signaling of Ca(2+) channels in cerebral arterioles

Smoking is a major health hazard with proven deleterious effects on the cerebral circulation, including a decrease in cerebral blood flow and a high risk for stroke. To elucidate cellular mechanisms for the vasoconstrictive and pathological effects of nicotine, we used a nystatin-perforated patch-clamp technique to study Ca(2+) channels and Ca(2+)-activated K(+) (BK) channels in smooth muscle cells isolated from cerebral lenticulostriate arterioles of rats chronically exposed to nicotine (4.5 mg/kg per day of nicotine free base, 15 to 22 days via osmotic minipump). Two major effects were observed in cells from nicotine-treated animals compared with controls. First, Ca(2+) channels were upregulated (0.48+/-0.03 pS/pF [20 cells] versus 0.35+/-0.01 pS/pF [31 cells], P:<0.005) and BK channels were downregulated (12+/-3 pA/pF [14 cells] versus 34+/-7 pA/pF [14 cells], P:<0.05), mimicking the effect of an apparent decrease in bioavailability of endogenous NO. Second, normal downregulation of Ca(2+) channels by exogenous NO (sodium nitroprusside [SNP], 100 nmol/L) and cGMP (8-bromo-cGMP, 0.1 mmol/L) was absent, whereas normal upregulation of BK channels by these agents was preserved, suggesting block of NO signaling downstream of cGMP-dependent protein kinase. In pial window preparations, chronic nicotine blunted NO-induced vasodilation of pial vessels and the increase in cortical blood flow measured by laser-Doppler flowmetry, demonstrating the importance of Ca(2+) channel downregulation in NO-induced vasorelaxation. These findings elucidate a new pathophysiological mechanism involving altered Ca(2+) homeostasis in cerebral arterioles that may predispose to stroke.

Ca2+ channels, 'quantized' Ca2+ release, and differentiation of myocytes in the cardiovascular system

The application of confocal microscopy to cardiac and skeletal muscle has resulted in the observation of transient, spatially localized elevations in [Ca2+]i, termed 'Ca2+ sparks'. Ca2+ sparks are thought to represent 'elementary' Ca2+ release events, which arise from one or more ryanodine receptor (RyR) channels in the sarcoplasmic reticulum. In cardiac muscle, Ca2+ sparks appear to be key elements of excitation-contraction coupling, in which the global [Ca2+]i transient is thought to involve the recruitment of Ca2+ sparks, each of which is controlled locally by single coassociated L-type Ca2+ channels. Recently, Ca2+ sparks have been detected in smooth muscle cells of arteries. In this review, we analyse the complex relationship of Ca2+ influx and Ca2+ release with local, subcellular Ca2+ microdomains in light of recent studies on Ca2+ sparks in cardiovascular cells. We performed a comparative analysis of 'elementary' Ca2+ release units in mouse, rat and human arterial smooth muscle cells, using measurements of Ca2+ sparks and plasmalemmal K(Ca) currents activated by Ca2+ sparks (STOCs). Furthermore, the appearance of Ca2+ sparks during ontogeny of arterial smooth muscle is explored. Using intact pressurized arteries, we have investigated whether RyRs causing Ca2+ sparks (but not smaller 'quantized' Ca2+ release events, e.g. hypothetical 'Ca2+ quarks') function as key signals that, through membrane potential and global cytoplasmic [Ca2+], oppose arterial myogenic tone and influence vasorelaxation. We believe that voltage-dependent Ca2+ channels and local RyR-related Ca2+ signals are important in differentiation, proliferation, and gene expression. Our findings suggest that 'elementary' Ca2+ release units may represent novel potent therapeutic targets for regulating function of intact arterial smooth muscle tissue.

Ion channels and the control of blood pressure

Ion channels exist in all cells and are enormously varied in structure, function and regulation. Some progress has been made in understanding the role that ion channels play in the control of blood pressure, but the discipline is still in its infancy. Ion channels provide many different targets for intervention in disorders of blood pressure and exciting advances have been made in this field. It is possible that new drugs, as well as antisense nucleotide technology or gene therapy directed towards ion channels, may form a new class of treatments for high and low blood pressure in the future.