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McGarr GW, Muia CM, Saci S, Fujii N, Kenny GP. K Ca channels are major contributors to ATP-induced cutaneous vasodilation in healthy older adults. Microvasc Res 2020; 133:104096. [PMID: 33058899 DOI: 10.1016/j.mvr.2020.104096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2020] [Revised: 08/30/2020] [Accepted: 10/08/2020] [Indexed: 11/19/2022]
Abstract
OBJECTIVE To examine the contributions of calcium-activated K+ (KCa) channels and nitric oxide synthase (NOS) to adenosine triphosphate (ATP)-induced cutaneous vasodilation in healthy older adults. METHODS In eleven older adults (69 ± 2 years, 5 females), cutaneous vascular conductance, normalized to maximum vasodilation (%CVCmax) was assessed at four dorsal forearm skin sites that were continuously perfused with either 1) lactated Ringer solution (Control), 2) 50 mM tetraethylammonium (TEA, KCa channel blocker), 3) 10 mM Nω-nitro-L-arginine (L-NNA, NOS inhibitor), or 4) combined 50 mM TEA +10 mM L-NNA, via microdialysis. Local skin temperature was fixed at 33 °C at all sites with local heaters throughout the protocol while the cutaneous vasodilator response was assessed during coadministration of ATP (0.03, 0.3, 3, 30, 300 mM; 20 min per dose), followed by 50 mM sodium nitroprusside and local skin heating to 43 °C to achieve maximum vasodilation (20-30 min). RESULTS Blockade of KCa channels blunted %CVCmax relative to Control from 0.3 to 300 mM ATP (All P < 0.05). A similar response was observed for the combined KCa channel blockade and NOS inhibition site from 3 to 300 mM ATP (All P < 0.05). Conversely, NOS inhibition alone did not influence %CVCmax across all ATP doses (All P > 0.05). CONCLUSION In healthy older adults, KCa channels play an important role in modulating ATP-induced cutaneous vasodilation, while the NOS contribution to this response is negligible.
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Fan C, Sukomon N, Flood E, Rheinberger J, Allen TW, Nimigean CM. Ball-and-chain inactivation in a calcium-gated potassium channel. Nature 2020; 580:288-293. [PMID: 32269335 PMCID: PMC7153497 DOI: 10.1038/s41586-020-2116-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 01/15/2020] [Indexed: 01/21/2023]
Abstract
Inactivation is the process by which ion channels terminate ion flux through their pores while the opening stimulus is still present1. In neurons, inactivation of both sodium and potassium channels is crucial for the generation of action potentials and regulation of firing frequency1,2. A cytoplasmic domain of either the channel or an accessory subunit is thought to plug the open pore to inactivate the channel via a 'ball-and-chain' mechanism3-7. Here we use cryo-electron microscopy to identify the molecular gating mechanism in calcium-activated potassium channels by obtaining structures of the MthK channel from Methanobacterium thermoautotrophicum-a purely calcium-gated and inactivating channel-in a lipid environment. In the absence of Ca2+, we obtained a single structure in a closed state, which was shown by atomistic simulations to be highly flexible in lipid bilayers at ambient temperature, with large rocking motions of the gating ring and bending of pore-lining helices. In Ca2+-bound conditions, we obtained several structures, including multiple open-inactivated conformations, further indication of a highly dynamic protein. These different channel conformations are distinguished by rocking of the gating rings with respect to the transmembrane region, indicating symmetry breakage across the channel. Furthermore, in all conformations displaying open channel pores, the N terminus of one subunit of the channel tetramer sticks into the pore and plugs it, with free energy simulations showing that this is a strong interaction. Deletion of this N terminus leads to functionally non-inactivating channels and structures of open states without a pore plug, indicating that this previously unresolved N-terminal peptide is responsible for a ball-and-chain inactivation mechanism.
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Xu J, Zeug A, Riederer B, Yeruva S, Griesbeck O, Daniel H, Tuo B, Ponimaskin E, Dong H, Seidler U. Calcium-sensing receptor regulates intestinal dipeptide absorption via Ca 2+ signaling and IK Ca activation. Physiol Rep 2020; 8:e14337. [PMID: 31960592 PMCID: PMC6971415 DOI: 10.14814/phy2.14337] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Although absorption of di- and tripeptides into intestinal epithelial cells occurs via the peptide transporter 1 (PEPT1, also called solute carrier family 15 member 1 (SLC15A1)), the detailed regulatory mechanisms are not fully understood. We examined: (a) whether dipeptide absorption in villous enterocytes is associated with a rise in cytosolic Ca2+ ([Ca2+ ]cyt ), (b) whether the calcium sensing receptor (CaSR) is involved in dipeptide-elicited [Ca2+ ]cyt signaling, and (c) what potential consequences of [Ca2+ ]cyt signaling may enhance enterocyte dipeptide absorption. Dipeptide Gly-Sar and CaSR agonist spermine markedly raised [Ca2+ ]cyt in villous enterocytes, which was abolished by NPS-2143, a selective CaSR antagonist and U73122, an phospholipase C (PLC) inhibitor. Apical application of Gly-Sar induced a jejunal short-circuit current (Isc), which was reduced by NPS-2143. CaSR expression was identified in the lamina propria and on the basal enterocyte membrane of mouse jejunal mucosa in both WT and Slc15a1-/- animals, but Gly-Sar-induced [Ca2+ ]cyt signaling was significantly decreased in Slc15a1-/- villi. Clotrimazole and TRM-34, two selective blockers of the intermediate conductance Ca2+ -activated K+ channel (IKCa ), but not iberiotoxin, a selective blocker of the large-conductance K+ channel (BKCa ) and apamin, a selective blocker of the small-conductance K+ channel (SKCa ), significantly inhibited Gly-Sar-induced Isc in native tissues. We reveal a novel CaSR-PLC-Ca2+ -IKCa pathway in the regulation of small intestinal dipeptide absorption, which may be exploited as a target for future drug development in human nutritional disorders.
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Dickerson MT, Dadi PK, Altman MK, Verlage KR, Thorson AS, Jordan KL, Vierra NC, Amarnath G, Jacobson DA. Glucose-mediated inhibition of calcium-activated potassium channels limits α-cell calcium influx and glucagon secretion. Am J Physiol Endocrinol Metab 2019; 316:E646-E659. [PMID: 30694690 PMCID: PMC6482666 DOI: 10.1152/ajpendo.00342.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pancreatic α-cells exhibit oscillations in cytosolic Ca2+ (Ca2+c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca2+c oscillations have not been elucidated. As β-cell Ca2+c oscillations are regulated in part by Ca2+-activated K+ (Kslow) currents, this work investigated the role of Kslow in α-cell Ca2+ handling and GCG secretion. α-Cells displayed Kslow currents that were dependent on Ca2+ influx through L- and P/Q-type voltage-dependent Ca2+ channels (VDCCs) as well as Ca2+ released from endoplasmic reticulum stores. α-Cell Kslow was decreased by small-conductance Ca2+-activated K+ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca2+-activated K+ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca2+-activated K+ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell Kslow with apamin depolarized membrane potential ( Vm) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca2+ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca2+ influx. Total α-cell Ca2+c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca2+c following prolonged Kslow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that Kslow activation provides a hyperpolarizing influence on α-cell Vm that sustains Ca2+ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca2+c is elevated during secretagogue stimulation, Kslow activation helps to preserve GCG secretion.
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Cocozza G, di Castro MA, Carbonari L, Grimaldi A, Antonangeli F, Garofalo S, Porzia A, Madonna M, Mainiero F, Santoni A, Grassi F, Wulff H, D'Alessandro G, Limatola C. Ca 2+-activated K + channels modulate microglia affecting motor neuron survival in hSOD1 G93A mice. Brain Behav Immun 2018; 73:584-595. [PMID: 29981425 PMCID: PMC6129409 DOI: 10.1016/j.bbi.2018.07.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2018] [Revised: 06/28/2018] [Accepted: 07/02/2018] [Indexed: 12/13/2022] Open
Abstract
Recent studies described a critical role for microglia in amyotrophic lateral sclerosis (ALS), where these CNS-resident immune cells participate in the establishment of an inflammatory microenvironment that contributes to motor neuron degeneration. Understanding the mechanisms leading to microglia activation in ALS could help to identify specific molecular pathways which could be targeted to reduce or delay motor neuron degeneration and muscle paralysis in patients. The intermediate-conductance calcium-activated potassium channel KCa3.1 has been reported to modulate the "pro-inflammatory" phenotype of microglia in different pathological conditions. We here investigated the effects of blocking KCa3.1 activity in the hSOD1G93AALS mouse model, which recapitulates many features of the human disease. We report that treatment of hSOD1G93A mice with a selective KCa3.1 inhibitor, 1-[(2-chlorophenyl)diphenylmethyl]-1H-pyrazole (TRAM-34), attenuates the "pro-inflammatory" phenotype of microglia in the spinal cord, reduces motor neuron death, delays onset of muscle weakness, and increases survival. Specifically, inhibition of KCa3.1 channels slowed muscle denervation, decreased the expression of the fetal acetylcholine receptor γ subunit and reduced neuromuscular junction damage. Taken together, these results demonstrate a key role for KCa3.1 in driving a pro-inflammatory microglia phenotype in ALS.
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Tiwari MN, Mohan S, Biala Y, Yaari Y. Differential contributions of Ca 2+ -activated K + channels and Na + /K + -ATPases to the generation of the slow afterhyperpolarization in CA1 pyramidal cells. Hippocampus 2018; 28:338-357. [PMID: 29431274 PMCID: PMC5947627 DOI: 10.1002/hipo.22836] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Revised: 12/17/2017] [Accepted: 02/05/2018] [Indexed: 12/13/2022]
Abstract
In many types of CNS neurons, repetitive spiking produces a slow afterhyperpolarization (sAHP), providing sustained, intrinsically generated negative feedback to neuronal excitation. Changes in the sAHP have been implicated in learning behaviors, in cognitive decline in aging, and in epileptogenesis. Despite its importance in brain function, the mechanisms generating the sAHP are still controversial. Here we have addressed the roles of M-type K+ current (IM ), Ca2+ -gated K+ currents (ICa(K) 's) and Na+ /K+ -ATPases (NKAs) current to sAHP generation in adult rat CA1 pyramidal cells maintained at near-physiological temperature (35 °C). No evidence for IM contribution to the sAHP was found in these neurons. Both ICa(K) 's and NKA current contributed to sAHP generation, the latter being the predominant generator of the sAHP, particularly when evoked with short trains of spikes. Of the different NKA isoenzymes, α1 -NKA played the key role, endowing the sAHP a steep voltage-dependence. Thus normal and pathological changes in α1 -NKA expression or function may affect cognitive processes by modulating the inhibitory efficacy of the sAHP.
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Mathew John C, Khaddaj Mallat R, George G, Kim T, Mishra RC, Braun AP. Pharmacologic targeting of endothelial Ca 2+-activated K + channels: A strategy to improve cardiovascular function. Channels (Austin) 2018; 12:126-136. [PMID: 29577810 PMCID: PMC5972810 DOI: 10.1080/19336950.2018.1454814] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2018] [Accepted: 03/15/2018] [Indexed: 12/17/2022] Open
Abstract
Endothelial small and intermediate-conductance, Ca2+-activated K+ channels (KCa2.3 and KCa3.1, respectively) play an important role in the regulation of vascular function and systemic blood pressure. Growing evidence indicates that they are intimately involved in agonist-evoked vasodilation of small resistance arteries throughout the circulation. Small molecule activators of KCa2.x and 3.1 channels, such as SKA-31, can acutely inhibit myogenic tone in isolated resistance arteries, induce effective vasodilation in intact vascular beds, such as the coronary circulation, and acutely decrease systemic blood pressure in vivo. The blood pressure-lowering effect of SKA-31, and early indications of improvement in endothelial dysfunction suggest that endothelial KCa channel activators could eventually be developed into a new class of endothelial targeted agents to combat hypertension or atherosclerosis. This review summarises recent insights into the activation of endothelial Ca2+ activated K+ channels in various vascular beds, and how tools, such as SKA-31, may be beneficial in disease-related conditions.
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Stowe DF, Yang M, Heisner JS, Camara AK. Endogenous and Agonist-induced Opening of Mitochondrial Big Versus Small Ca2+-sensitive K+ Channels on Cardiac Cell and Mitochondrial Protection. J Cardiovasc Pharmacol 2017; 70:314-328. [PMID: 28777255 PMCID: PMC5726766 DOI: 10.1097/fjc.0000000000000524] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Both big (BKCa) and small (SKCa) conductance Ca-sensitive K channels are present in mammalian cardiac cell mitochondria (m). We used pharmacological agonists and antagonists of BKCa and SKCa channels to examine the importance of endogenous opening of these channels and the relative contribution of either or both of these channels to protect against contractile dysfunction and reduce infarct size after ischemia reperfusion (IR) injury through a mitochondrial protective mechanism. After global cardiac IR injury of ex vivo perfused Guinea pig hearts, we found the following: both agonists NS1619 (for BKCa) and DCEB (for SKCa) improved contractility; BKCa antagonist paxilline (PAX) alone or with SKCa antagonist NS8593 worsened contractility and enhanced infarct size; both antagonists PAX and NS8593 obliterated protection by their respective agonists; BKCa and SKCa antagonists did not block protection afforded by SKCa and BKCa agonists, respectively; and all protective effects by the agonists were blocked by scavenging superoxide anions (O2) with Mn(III) tetrakis (4-benzoic acid) porphyrin (TBAP). Contractile function was inversely associated with global infarct size. In in vivo rats, infusion of NS8593, PAX, or both antagonists enhanced regional infarct size while infusion of either NS1619 or DCEB reduced infarct size. In cardiac mitochondria isolated from ex vivo hearts after IR, combined SKCa and BKCa agonists improved respiratory control index and Ca retention capacity compared with IR alone, whereas the combined antagonists did not alter respiratory control index but worsened Ca retention capacity. Although the differential protective bioenergetics effects of endogenous or exogenous BKCa and SKCa channel opening remain unclear, each channel likely responds to different sensing Ca concentrations and voltage gradients over time during oxidative stress-induced injury to individually or together protect cardiac mitochondria and myocytes.
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Honrath B, Krabbendam IE, Culmsee C, Dolga AM. Small conductance Ca 2+-activated K + channels in the plasma membrane, mitochondria and the ER: Pharmacology and implications in neuronal diseases. Neurochem Int 2017; 109:13-23. [PMID: 28511953 DOI: 10.1016/j.neuint.2017.05.005] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 04/24/2017] [Accepted: 05/08/2017] [Indexed: 12/14/2022]
Abstract
Ca2+-activated K+ (KCa) channels regulate after-hyperpolarization in many types of neurons in the central and peripheral nervous system. Small conductance Ca2+-activated K+ (KCa2/SK) channels, a subfamily of KCa channels, are widely expressed in the nervous system, and in the cardiovascular system. Voltage-independent SK channels are activated by alterations in intracellular Ca2+ ([Ca2+]i) which facilitates the opening of these channels through binding of Ca2+ to calmodulin that is constitutively bound to the SK2 C-terminus. In neurons, SK channels regulate synaptic plasticity and [Ca2+]i homeostasis, and a number of recent studies elaborated on the emerging neuroprotective potential of SK channel activation in conditions of excitotoxicity and cerebral ischemia, as well as endoplasmic reticulum (ER) stress and oxidative cell death. Recently, SK channels were discovered in the inner mitochondrial membrane and in the membrane of the endoplasmic reticulum which sheds new light on the underlying molecular mechanisms and pathways involved in SK channel-mediated protective effects. In this review, we will discuss the protective properties of pharmacological SK channel modulation with particular emphasis on intracellularly located SK channels as potential therapeutic targets in paradigms of neuronal dysfunction.
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Ozkor MA, Hayek SS, Rahman AM, Murrow JR, Kavtaradze N, Lin J, Manatunga A, Quyyumi AA. Contribution of endothelium-derived hyperpolarizing factor to exercise-induced vasodilation in health and hypercholesterolemia. Vasc Med 2015; 20:14-22. [PMID: 25648989 PMCID: PMC9135050 DOI: 10.1177/1358863x14565374] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The role of endothelium-derived hyperpolarizing factor (EDHF) in either the healthy circulation or in those with hypercholesterolemia is unknown. In healthy and hypercholesterolemic subjects, we measured forearm blood flow (FBF) using strain-gauge plethysmography at rest, during graded handgrip exercise, and after sodium nitroprusside infusion. Measurements were repeated after l-NMMA, tetraethylammonium (TEA), and combined infusions. At rest, l-NMMA infusion reduced FBF in healthy but not hypercholesterolemic subjects. At peak exercise, vasodilation was lower in hypercholesterolemic compared to healthy subjects (274% vs 438% increase in FBF, p=0.017). TEA infusion reduced exercise-induced vasodilation in both healthy and hypercholesterolemic subjects (27%, p<0.0001 and -20%, p<0.0001, respectively). The addition of l-NMMA to TEA further reduced FBF in healthy (-14%, p=0.012) but not in hypercholesterolemic subjects, indicating a reduced nitric oxide and greater EDHF-mediated contribution to exercise-induced vasodilation in hypercholesterolemia. In conclusion, exercise-induced vasodilation is impaired and predominantly mediated by EDHF in hypercholesterolemic subjects. CLINICAL TRIAL REGISTRATION IDENTIFIER NCT00166166:
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Modgil A, Guo L, O’Rourke ST, Sun C. Apelin-13 inhibits large-conductance Ca2+-activated K+ channels in cerebral artery smooth muscle cells via a PI3-kinase dependent mechanism. PLoS One 2013; 8:e83051. [PMID: 24386141 PMCID: PMC3873301 DOI: 10.1371/journal.pone.0083051] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2013] [Accepted: 11/04/2013] [Indexed: 11/25/2022] Open
Abstract
Apelin-13 causes vasoconstriction by acting directly on APJ receptors in vascular smooth muscle (VSM) cells; however, the ionic mechanisms underlying this action at the cellular level remain unclear. Large-conductance Ca2+-activated K+ (BKCa) channels in VSM cells are critical regulators of membrane potential and vascular tone. In the present study, we examined the effect of apelin-13 on BKCa channel activity in VSM cells, freshly isolated from rat middle cerebral arteries. In whole-cell patch clamp mode, apelin-13 (0.001-1 μM) caused concentration-dependent inhibition of BKCa in VSM cells. Apelin-13 (0.1 µM) significantly decreased BKCa current density from 71.25±8.14 pA/pF to 44.52±7.10 pA/pF (n=14 cells, P<0.05). This inhibitory effect of apelin-13 was confirmed by single channel recording in cell-attached patches, in which extracellular application of apelin-13 (0.1 µM) decreased the open-state probability (NPo) of BKCa channels in freshly isolated VSM cells. However, in inside-out patches, extracellular application of apelin-13 (0.1µM) did not alter the NPo of BKCa channels, suggesting that the inhibitory effect of apelin-13 on BKCa is not mediated by a direct action on BKCa. In whole cell patches, pretreatment of VSM cells with LY-294002, a PI3-kinase inhibitor, markedly attenuated the apelin-13-induced decrease in BKCa current density. In addition, treatment of arteries with apelin-13 (0.1 µM) significantly increased the ratio of phosphorylated-Akt/total Akt, indicating that apelin-13 significantly increases PI3-kinase activity. Taken together, the data suggest that apelin-13 inhibits BKCa channel via a PI3-kinase-dependent signaling pathway in cerebral artery VSM cells, which may contribute to its regulatory action in the control of vascular tone.
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Fan F, Sun CW, Maier KG, Williams JM, Pabbidi MR, Didion SP, Falck JR, Zhuo J, Roman RJ. 20-Hydroxyeicosatetraenoic acid contributes to the inhibition of K+ channel activity and vasoconstrictor response to angiotensin II in rat renal microvessels. PLoS One 2013; 8:e82482. [PMID: 24324797 PMCID: PMC3853207 DOI: 10.1371/journal.pone.0082482] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2013] [Accepted: 11/02/2013] [Indexed: 11/24/2022] Open
Abstract
The present study examined whether 20-hydroxyeicosatetraenoic acid (HETE) contributes to the vasoconstrictor effect of angiotensin II (ANG II) in renal microvessels by preventing activation of the large conductance Ca2+-activated K+ channel (KCa) in vascular smooth muscle (VSM) cells. ANG II increased the production of 20-HETE in rat renal microvessels. This response was attenuated by the 20-HETE synthesis inhibitors, 17-ODYA and HET0016, a phospholipase A2 inhibitor AACOF3, and the AT1 receptor blocker, Losartan, but not by the AT2 receptor blocker, PD123319. ANG II (10-11 to 10-6 M) dose-dependently decreased the diameter of renal microvessels by 41 ± 5%. This effect was blocked by 17-ODYA. ANG II (10-7 M) did not alter KCa channel activity recorded from cell-attached patches on renal VSM cells under control conditions. However, it did reduce the NPo of the KCa channel by 93.4 ± 3.1% after the channels were activated by increasing intracellular calcium levels with ionomycin. The inhibitory effect of ANG II on KCa channel activity in the presence of ionomycin was attenuated by 17-ODYA, AACOF3, and the phospholipase C (PLC) inhibitor U-73122. ANG II induced a peak followed by a steady-state increase in intracellular calcium concentration in renal VSM cells. 17-ODYA (10-5 M) had no effect on the peak response, but it blocked the steady-state increase. These results indicate that ANG II stimulates the formation of 20-HETE in rat renal microvessels via the AT1 receptor activation and that 20-HETE contributes to the vasoconstrictor response to ANG II by blocking activation of KCa channel and facilitating calcium entry.
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MESH Headings
- Angiotensin II/pharmacology
- Animals
- Calcium/metabolism
- Gene Expression
- Hydroxyeicosatetraenoic Acids/metabolism
- Ionomycin/pharmacology
- Male
- Microvessels/drug effects
- Microvessels/metabolism
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Phospholipases A2/metabolism
- Potassium Channel Blockers/pharmacology
- Potassium Channels/metabolism
- Potassium Channels, Calcium-Activated/antagonists & inhibitors
- Potassium Channels, Calcium-Activated/metabolism
- Rats
- Receptors, Angiotensin/genetics
- Receptors, Angiotensin/metabolism
- Renal Circulation/drug effects
- Renal Circulation/physiology
- Type C Phospholipases/metabolism
- Vasoconstrictor Agents/pharmacology
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Tricarico D, Mele A, Calzolaro S, Cannone G, Camerino GM, Dinardo MM, Latorre R, Conte Camerino D. Emerging role of calcium-activated potassium channel in the regulation of cell viability following potassium ions challenge in HEK293 cells and pharmacological modulation. PLoS One 2013; 8:e69551. [PMID: 23874973 PMCID: PMC3712936 DOI: 10.1371/journal.pone.0069551] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2013] [Accepted: 06/10/2013] [Indexed: 11/18/2022] Open
Abstract
Emerging evidences suggest that Ca2+activated-K+-(BK) channel is involved in the regulation of cell viability. The changes of the cell viability observed under hyperkalemia (15 mEq/L) or hypokalemia (0.55 mEq/L) conditions were investigated in HEK293 cells expressing the hslo subunit (hslo-HEK293) in the presence or absence of BK channel modulators. The BK channel openers(10-11-10-3M) were: acetazolamide(ACTZ), Dichlorphenamide(DCP), methazolamide(MTZ), bendroflumethiazide(BFT), ethoxzolamide(ETX), hydrochlorthiazide(HCT), quercetin(QUERC), resveratrol(RESV) and NS1619; and the BK channel blockers(2x10-7M-5x10-3M) were: tetraethylammonium(TEA), iberiotoxin(IbTx) and charybdotoxin(ChTX). Experiments on cell viability and channel currents were performed using cell counting kit-8 and patch-clamp techniques, respectively. Hslo whole-cell current was potentiated by BK channel openers with different potency and efficacy in hslo-HEK293. The efficacy ranking of the openers at -60 mV(Vm) was BFT> ACTZ >DCP ≥RESV≥ ETX> NS1619> MTZ≥ QUERC; HCT was not effective. Cell viability after 24 h of incubation under hyperkalemia was enhanced by 82+6% and 33+7% in hslo-HEK293 cells and HEK293 cells, respectively. IbTx, ChTX and TEA enhanced cell viability in hslo-HEK293. BK openers prevented the enhancement of the cell viability induced by hyperkalemia or IbTx in hslo-HEK293 showing an efficacy which was comparable with that observed as BK openers. BK channel modulators failed to affect cell currents and viability under hyperkalemia conditions in the absence of hslo subunit. In contrast, under hypokalemia cell viability was reduced by -22+4% and -23+6% in hslo-HEK293 and HEK293 cells, respectively; the BK channel modulators failed to affect this parameter in these cells. In conclusion, BK channel regulates cell viability under hyperkalemia but not hypokalemia conditions. BFT and ACTZ were the most potent drugs either in activating the BK current and in preventing the cell proliferation induced by hyperkalemia. These findings may have relevance in disorders associated with abnormal K+ ion homeostasis including periodic paralysis and myotonia.
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Yang D, Arifhodzic L, Ganellin CR, Jenkinson DH. Further studies on bis-charged tetraazacyclophanes as potent inhibitors of small conductance Ca(2+)-activated K+ channels. Eur J Med Chem 2013; 63:907-23. [PMID: 23685886 DOI: 10.1016/j.ejmech.2013.02.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2013] [Revised: 02/21/2013] [Accepted: 02/22/2013] [Indexed: 11/20/2022]
Abstract
Previously, quinolinium-based tetraazacyclophanes, such as UCL 1684 and UCL 1848, have been shown to be extraordinarily sensitive to changes in chemical structure (especially to the size of the cyclophane system) with respect to activity as potent non-peptidic blockers of the small conductance Ca(2+)-activated K(+) ion channels (SKCa). The present work has sought to optimize the structure of the linking chains in UCL 1848. We report the synthesis and SKCa channel-blocking activity of 29 analogues of UCL 1848 in which the central CH2 of UCL 1848 is replaced by other groups X or Y = O, S, CF2, CO, CHOH, CC, CHCH, CHMe to explore whether subtle changes in bond length or flexibility can improve potency still further. The possibility of improving potency by introducing ring substituents has also been explored by synthesizing and testing 25 analogues of UCL 1684 and UCL 1848 with substituents (NO2, NH2, CF3, F, Cl, CH3, OCH3, OCF3, OH) in the 5, 6 or 7 positions of the aminoquinolinium rings. As in our earlier work, each compound was assayed for inhibition of the afterhyperpolarization (AHP) in rat sympathetic neurons, an action mediated by the SK3 subtype of the SKCa channel. One of the new compounds (39, R(7) = Cl, UCL 2053) is twice as potent as UCL 1848 and UCL 1684: seven are comparable in activity.
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15
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Gao Q, Hu J, Hu J, Yu Y, Ye H, Li Z, Guan S. Calcium activated potassium channel and protein kinase C participate in the cardiac protection of remote post conditioning. PAKISTAN JOURNAL OF PHARMACEUTICAL SCIENCES 2013; 26:285-290. [PMID: 23455198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The present study was designed to investigate the roles of Ca(2+) activated K(+) channel (KCa) and protein kinase C (PKC) in the protective mechanisms of remote ischemic post conditioning (RPostC) when rat heart was subjected to ischemia/reperfusion (I/R) injury in vivo. Rat heart was subjected to regional ischemia for 45 min and reperfusion for 180 min in vivo to mimic I/R injury. RPostC was induced by 5 min right femoral artery occlusion followed by 5 min reperfusion for 3 cycles (totally 30 min) after 15 min of cardiac ischemia. Delayed remote ischemic post conditioning (delayed RPostC) was induced after 10 min of cardiac reperfusion. The hemodynamic parameters including mean arterial blood pressure and heart rate (HR) were recorded, and lactate dehydrogenase (LDH) release in plasma and infarct size were determined, and arrhythmia scores were calculated. In contrast to I/R, RPostC reduced infarct size and LDH release during reperfusion, the occurrence of arrhythmia was decreased, but no changes in delayed RPostC. The specific inhibitor of KCa iberiotoxin and PKC inhibitor chelerythrine both attenuated the role of RPostC. The findings indicated that RPostC had a protective effect on myocardial ischemia/reperfusion injury. Opening of KCa and activating of PKC may be involved in the mechanisms of RPostC.
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16
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Brereton MF, Wareing M, Jones RL, Greenwood SL. Characterisation of K+ channels in human fetoplacental vascular smooth muscle cells. PLoS One 2013; 8:e57451. [PMID: 23437391 PMCID: PMC3578819 DOI: 10.1371/journal.pone.0057451] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2012] [Accepted: 01/24/2013] [Indexed: 11/18/2022] Open
Abstract
Adequate blood flow through placental chorionic plate resistance arteries (CPAs) is necessary for oxygen and nutrient transfer to the fetus and a successful pregnancy. In non-placental vascular smooth muscle cells (SMCs), K(+) channels regulate contraction, vascular tone and blood flow. Previous studies showed that K(+) channel modulators alter CPA tone, but did not distinguish between effects on K(+) channels in endothelial cells and SMCs. In this study, we developed a preparation of freshly isolated CPASMCs of normal pregnancy and investigated K(+) channel expression and function. CPASMCs were isolated from normal human term placentas using enzymatic digestion. Purity and phenotype was confirmed with immunocytochemistry. Whole-cell patch clamp was used to assess K(+) channel currents, and mRNA and protein expression was determined in intact CPAs and isolated SMCs with RT-PCR and immunostaining. Isolated SMCs expressed α-actin but not CD31, a marker of endothelial cells. CPASMCs and intact CPAs expressed h-caldesmon and non-muscle myosin heavy chain-2; phenotypic markers of contractile and synthetic SMCs respectively. Whole-cell currents were inhibited by 4-AP, TEA, charybdotoxin and iberiotoxin implicating functional K(v) and BK(Ca) channels. 1-EBIO enhanced whole cell currents which were abolished by TRAM-34 and reduced by apamin indicating activation of IK(Ca) and SK(Ca) respectively. BK(Ca), IK(Ca) and SK(Ca)3 mRNA and/or protein were expressed in CPASMCs and intact CPAs. This study provides the first direct evidence for functional K(v), BK(Ca,) IK(Ca) and SK(Ca) channels in CPASMCs. These cells display a mixed phenotype implicating a dual role for CPASMCs in controlling both fetoplacental vascular resistance and vasculogenesis.
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MESH Headings
- Actins/genetics
- Actins/metabolism
- Calcium/metabolism
- Calmodulin-Binding Proteins/genetics
- Calmodulin-Binding Proteins/metabolism
- Chorion/blood supply
- Chorion/cytology
- Chorion/drug effects
- Chorion/metabolism
- Female
- Fetus
- Gene Expression/drug effects
- Humans
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/drug effects
- Muscle, Smooth, Vascular/metabolism
- Myocytes, Smooth Muscle/cytology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/metabolism
- Myosin Heavy Chains/genetics
- Myosin Heavy Chains/metabolism
- Patch-Clamp Techniques
- Placenta/blood supply
- Placenta/cytology
- Placenta/drug effects
- Placenta/metabolism
- Potassium/metabolism
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Calcium-Activated/antagonists & inhibitors
- Potassium Channels, Calcium-Activated/classification
- Potassium Channels, Calcium-Activated/genetics
- Potassium Channels, Calcium-Activated/metabolism
- Potassium Channels, Voltage-Gated/antagonists & inhibitors
- Potassium Channels, Voltage-Gated/classification
- Potassium Channels, Voltage-Gated/genetics
- Potassium Channels, Voltage-Gated/metabolism
- Pregnancy
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Shimanskaia TV, Strutinskaia NA, Vavilova GL, Goshovskaia IV, Semenikhina EN, Sagach VF. [Cyclosporin A-sensitive mitochondrial pore as a target of cardioprotective action of hydrogen sulfide donor]. ROSSIISKII FIZIOLOGICHESKII ZHURNAL IMENI I.M. SECHENOVA 2013; 99:261-272. [PMID: 23650739] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
In experiments on a model of ischemia-reperfusion in Langendorff isolated rat hearts and isolated mitochondria we studied the role of hydrogen sulfide donor - sodium hydrosulfide (NaHS, 7.4 mg/kg) in modulating the sensitivity ofmitochondrial permeability transition pore opening. It was shown that NaHS increased the reserves of rat myocardium and had cardioprotective effects from ischemia-reperfusion. In experiments on isolated mitochondria NaHS in concentrations of 10(-6), 10(-5) and 5 x 10(-5) mol/L inhibited Ca(2+)-induced swelling of mitochondria. Preincubation of isolated mitochondria with K+(ATphi)-channels inhibitor 5-hydroxydecanoate (10(-4) mol/L) reduced the protective effect of NaHS (10(-5) mol/L). Thus, we consider that NaHS protective effect from reperfusion disturbances of heart function was realized via inhibition of Ca(2+)-induced mitochondrial permeability transition pore opening.
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18
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Sitdikova GF, Khaertdinov NN, Zefirov AL. Role of calcium and potassium channels in effects of hydrogen sulfide on frog myocardial contractility. Bull Exp Biol Med 2012; 151:163-6. [PMID: 22238741 DOI: 10.1007/s10517-011-1280-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
The effects of sodium hydrosulfide NaHS, a donor of hydrogen sulfide H2S, on the force of muscle contraction were examined on isolated myocardial strips from frog ventricles. NaHS decreased the amplitude of muscle contractions in a dose-dependent manner under normal conditions and during inhibition of Ca channels with nifedipine. In contrast, under conditions of blockade of ATP-dependent potassium channels with glibenclamide, NaHS exerted a positive inotropic effect from the first minute of application. Neither blockade, nor activation of ATP-dependent K-channels with glibenclamide modulated the negative inotropic effect of NaHS. Inhibition of K-channels with tetraethylammonium (TEA) (3, 5, 10 mM) or 4-aminopyridine increased the amplitude of myocardial contractions. Preliminary application of 4-aminopyridine or TEA (3 mM) did not eliminate NaHS-induced negative inotropic effect, although higher TEA concentrations (5 or 10 mM) prevented it. The data indicate that the targets of H(2)S in frog myocardium are ATP-dependent, Ca-activated, and voltage-dependent K-channels.
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Buxton SK, Neveu C, Charvet CL, Robertson AP, Martin RJ. On the mode of action of emodepside: slow effects on membrane potential and voltage-activated currents in Ascaris suum. Br J Pharmacol 2011; 164:453-70. [PMID: 21486286 PMCID: PMC3188918 DOI: 10.1111/j.1476-5381.2011.01428.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2010] [Revised: 01/17/2011] [Accepted: 03/28/2011] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND AND PURPOSE Anthelmintics are required for treatment and prophylaxis of nematode parasites of humans and domestic animals. Emodepside, a cyclooctadepsipeptide, is a modern anthelmintic that has a novel mode of action involving a Ca-activated K channel (SLO-1) in Caenorhabditis elegans, sometimes mediated by a latrophilin (LAT) receptor. We examined mechanisms of action of emodepside in a parasitic nematode, Ascaris suum. EXPERIMENTAL APPROACH RT-PCR was used to investigate expression of slo-1 and lat-1 in A. suum muscle flaps, and two-micropipette current-clamp and voltage-clamp techniques were used to record electrophysiological effects of emodepside. KEY RESULTS Expression of slo-1 and lat-1 were detected. Emodepside produced a slow time-dependent (20 min), 4-aminopyridine sensitive, concentration-dependent hyperpolarization and increase in voltage-activated K currents. Sodium nitroprusside increased the hyperpolarizations and K currents. N-nitro-L-arginine inhibited the hyperpolarizations and K currents. Phorbol-12-myristate-13 acetate increased the K currents, while staurosporine inhibited the hyperpolarizations and K currents. Iberiotoxin reduced these emodepside K currents. The effect of emodepside was reduced in Ca-free solutions. Emodepside had no effect on voltage-activated Ca currents. CONCLUSIONS AND IMPLICATIONS Asu-slo-1 and Asu-lat-1 are expressed in adult A. suum muscle flaps and emodepside produces slow activation of voltage-activated Ca-dependent SLO-1-like K channels. The effect of emodepside was enhanced by stimulation of protein kinase C and NO pathways. The data are consistent with a model in which NO, PKC and emodepside signalling pathways are separate and converge on the K channels, or in which emodepside activates NO and PKC signalling pathways to increase opening of the K channels.
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Beleznai TZ, Yarova PL, Yuill KH, Dora KA. Smooth muscle Ca(2+) -activated and voltage-gated K+ channels modulate conducted dilation in rat isolated small mesenteric arteries. Microcirculation 2011; 18:487-500. [PMID: 21535295 PMCID: PMC4826745 DOI: 10.1111/j.1549-8719.2011.00109.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
OBJECTIVE To assess the influence of blocking smooth muscle large conductance Ca(2+) -activated K+ channels and voltage-gated K+ channels on the conducted dilation to ACh and isoproterenol. MATERIALS AND METHODS Rat mesenteric arteries were isolated with a bifurcation, triple-cannulated, pressurized and imaged using confocal microscopy. Phenylephrine was added to the superfusate to generate tone, and agonists perfused into a sidebranch to evoke local dilation and subsequent conducted dilation into the feed artery. RESULTS Both ACh- and isoproterenol-stimulated local and conducted dilation with similar magnitudes of decay with distance along the feed artery (2000μm: ∼15% maximum dilation). The gap junction uncoupler carbenoxolone prevented both conducted dilation and intercellular spread of dye through gap junctions. IbTx, TEA or 4-AP, blockers of large conductance Ca(2+) -activated K+ channels and voltage-gated K+ channels, did not affect conducted dilation to either agonist. A combination of either IbTx or TEA with 4-AP markedly improved the extent of conducted dilation to both agonists (2000μm: >50% maximum dilation). The enhanced conducted dilation was reflected in the hyperpolarization to ACh (2000μm: Control, 4±1 mV, n = 3; TEA with 4-AP, 14±3mV, n=4), and was dependent on the endothelium. CONCLUSIONS These data show that activated BK(Ca) and K(V) -channels serve to reduce the effectiveness of conducted dilation.
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21
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Tishkin SM, Rekalov VV, Ivanova IV, MoreLand RS, Soloviev AI. Ionizing non-fatal whole-body irradiation inhibits Ca2+-dependent K+channels in endothelial cells of rat coronary artery: Possible contribution to depression of endothelium-dependent vascular relaxation. Int J Radiat Biol 2009; 83:161-9. [PMID: 17378524 DOI: 10.1080/09553000601146931] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
PURPOSE The goal of this study was to evaluate the influence of ionizing irradiation on large conductance Ca2+-dependent potassium (BKCa) channels in rat coronary endothelial cells. MATERIALS AND METHODS Rats were exposed to a 6 Gy dose from a cobalt60 source. Experimental design of this study comprised recording of contractile force using isolated rat aortic rings and whole-cell patch clamp techniques to study whole-cell potassium currents in isolated rat coronary artery endothelial cells. RESULTS It has been shown that outward potassium currents in endothelial cells 9 days after irradiation appear to be suppressed or even totally abolished. The reversal potential for these currents in irradiated cells was shifted to more positive values. Paxilline (500 nM), an inhibitor of BKCa channels, had no or only a negligible effect on irradiated cells. The experiments using isolated aortic rings demonstrated that both paxilline and irradiation significantly shifted the acetylcholine dependent concentration-relaxation response curve to the right. Irradiated tissues were insensitive to paxilline. CONCLUSION The results suggest that non-fatal, whole-body gamma-irradiation suppresses large conductance, calcium-activated potassium channels, which control the driving force for Ca2+ entry and therefore Ca2+ dependent nitric oxide (NO) synthesis in endothelial cells. This may contribute, in part, to radiation-induced endothelium dysfunction and an increase in arterial blood pressure.
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22
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Waring DW, Turgeon JL. Ca2+-activated K+ channels in gonadotropin-releasing hormone-stimulated mouse gonadotrophs. Endocrinology 2009; 150:2264-72. [PMID: 19106218 PMCID: PMC2671892 DOI: 10.1210/en.2008-1442] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
GnRH receptor activation elicits release of intracellular Ca(2+), which leads to secretion and also activates Ca(2+)-activated ion channels underlying membrane voltage changes. The predominant Ca(2+)-activated ion channels in rat and mouse gonadotrophs are Ca(2+)-activated K(+) channels. To establish the temporal relationship between GnRH-induced changes in intracellular [Ca(2+)] ([Ca(2+)](i)) and membrane current (I(m)), and to identify specific Ca(2+)-activated K(+) channels linking GnRH-induced increase in [Ca(2+)](i) to changes in plasma membrane electrical activity, we used single female mouse gonadotrophs in the perforated patch configuration of the patch-clamp technique, which preserves signaling pathways. Simultaneous measurement of [Ca(2+)](i) and I(m) in voltage-clamped gonadotrophs revealed that GnRH stimulates an increase in [Ca(2+)](i) that precedes outward I(m), and that activates two kinetically distinct currents identified, using specific toxin inhibitors, as small conductance Ca(2+)-activated K(+) (SK) current (I(SK)) and large (big) conductance voltage- and Ca(2+)-activated K(+) (BK) current (I(BK)). We show that the apamin-sensitive current has an IC(50) of 69 pM, consistent with the SK2 channel subtype and confirmed by immunocytochemistry. The magnitude of the SK current response to GnRH was attenuated by 17beta-estradiol (E(2)) pretreatment. Iberiotoxin, an inhibitor of BK channels, completely blocked the residual apamin-insensitive outward I(m), substantiating that I(BK) is a component of the GnRH-induced outward I(m). In contrast to its suppression of I(SK), E(2) pretreatment augmented peak I(BK). SK or BK channel inhibition modulated GnRH-stimulated LH secretion, implicating a role for these channels in gonadotroph function. In summary, in mouse gonadotrophs the GnRH-stimulated increase in [Ca(2+)](i) activates I(SK) and I(BK), which are differentially regulated by E(2) and which may be targets for E(2) positive feedback in LH secretion.
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Tharp DL, Bowles DK. The intermediate-conductance Ca2+ -activated K+ channel (KCa3.1) in vascular disease. Cardiovasc Hematol Agents Med Chem 2009; 7:1-11. [PMID: 19149539 DOI: 10.2174/187152509787047649] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
The intermediate-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) was first described by Gardos in erythrocytes and later confirmed to play a significant role in T-cell activation and the immune response. More recently, K(Ca)3.1 has been characterized in numerous cell types which contribute to the development of vascular disease, such as T-cells, B-cells, endothelial cells, fibroblasts, macrophages, and dedifferentiated smooth muscle cells (SMCs). Physiologically, K(Ca)3.1 has been demonstrated to play a role in acetylcholine and endothelium-derived hyperpolarizing factor (EDHF) induced hyperpolarization, and thus control of blood pressure. Pathophysiologically, K(Ca)3.1 contributes to proliferation of T-cells, B-cells, fibroblasts, and vascular SMCs, as well as the migration of SMCs and macrophages and platelet coagulation. Recent studies have indicated that blockade of K(Ca)3.1, by specific blockers such as TRAM-34, could prove to be an effective treatment for vascular disease by inhibiting T-cell activation as well as preventing proliferation and migration of macrophages, endothelial cells, and SMCs. This vasculoprotective potential of K(Ca)3.1 inhibition has been confirmed in both rodent and swine models of restenosis. In this review, we will discuss the physiological and pathophysiological role of K(Ca)3.1 in cells closely associated with vascular biology, and the effect of K(Ca)3.1 blockers on the initiation and progression of vascular disease.
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Hirukawa K, Muraki K, Ohya S, Imaizumi Y, Togari A. Electrophysiological properties of a novel Ca(2+)-activated K(+) channel expressed in human osteoblasts. Calcif Tissue Int 2008; 83:222-9. [PMID: 18787886 DOI: 10.1007/s00223-008-9167-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/06/2008] [Accepted: 08/04/2008] [Indexed: 11/28/2022]
Abstract
Intracellular Ca(2+) mobilization plays important roles in cell survival, proliferation, and differentiation of osteoblasts. In this study, we identified a novel type of Ca(2+)-activated K(+) channel in human osteoblasts and investigated its physiological roles. Using RT-PCR methods and single-channel analysis in the patch-clamp technique, we found that BK and IK channels were genetically expressed in human osteoblasts and had electrophysiological properties similar to those reported previously for the channels in other organs (conductance, voltage dependence, and sensitivity to intracellular Ca(2+)). Taking advantage of the fact that ATP induces elevation of the intracellular Ca(2+) concentration in human osteoblasts, we successfully demonstrated that ATP-induced hyperpolarization was effectively inhibited by the IK channel blockers charybdotoxin and clotrimazole and by a P2 purinergic receptor antagonist, suramin, but not by the BK channel blockers tetraethylammonium chloride and iberiotoxin under the current-clamp mode of whole-cell clamp. The present study is the first to demonstrate the electrophysiological properties and functional expression of IK channels in human osteoblasts, findings which suggest that IK channels are regulators of membrane potential that give rise to intracellular Ca(2+) mobilization by physiological stimulation.
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25
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Awumey EM, Hill SK, Diz DI, Bukoski RD. Cytochrome P-450 metabolites of 2-arachidonoylglycerol play a role in Ca2+-induced relaxation of rat mesenteric arteries. Am J Physiol Heart Circ Physiol 2008; 294:H2363-70. [PMID: 18375719 PMCID: PMC10433144 DOI: 10.1152/ajpheart.01042.2007] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The perivascular sensory nerve (PvN) Ca(2+)-sensing receptor (CaR) is implicated in Ca(2+)-induced relaxation of isolated, phenylephrine (PE)-contracted mesenteric arteries, which involves the vascular endogenous cannabinoid system. We determined the effect of inhibition of diacylglycerol (DAG) lipase (DAGL), phospholipase A(2) (PLA(2)), and cytochrome P-450 (CYP) on Ca(2+)-induced relaxation of PE-contracted rat mesenteric arteries. Our findings indicate that Ca(2+)-induced vasorelaxation is not dependent on the endothelium. The DAGL inhibitor RHC 802675 (1 microM) and the CYP and PLA(2) inhibitors quinacrine (5 microM) (EC(50): RHC 802675 2.8 +/- 0.4 mM vs. control 1.4 +/- 0.3 mM; quinacrine 4.8 +/- 0.4 mM vs. control 2.0 +/- 0.3 mM; n = 5) and arachidonyltrifluoromethyl ketone (AACOCF(3), 1 microM) reduced Ca(2+)-induced relaxation of mesenteric arteries. Synthetic 2-arachidonoylglycerol (2-AG) and glycerated epoxyeicosatrienoic acids (GEETs) induced concentration-dependent relaxation of isolated arteries. 2-AG relaxations were blocked by iberiotoxin (IBTX) (EC(50): control 0.96 +/- 0.14 nM, IBTX 1.3 +/- 0.5 microM) and miconazole (48 +/- 3%), and 11,12-GEET responses were blocked by IBTX (EC(50): control 55 +/- 9 nM, IBTX 690 +/- 96 nM) and SR-141716A. The data suggest that activation of the CaR in the PvN network by Ca(2+) leads to synthesis and/or release of metabolites of the CYP epoxygenase pathway and metabolism of DAG to 2-AG and subsequently to GEETs. The findings indicate a role for 2-AG and its metabolites in Ca(2+)-induced relaxation of resistance arteries; therefore this receptor may be a potential target for the development of new vasodilator compounds for antihypertensive therapy.
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MESH Headings
- 8,11,14-Eicosatrienoic Acid/metabolism
- Acetylcholine/pharmacology
- Animals
- Arachidonic Acids/metabolism
- Arachidonic Acids/pharmacology
- Calcium/metabolism
- Cytochrome P-450 Enzyme Inhibitors
- Cytochrome P-450 Enzyme System/metabolism
- Dose-Response Relationship, Drug
- Endocannabinoids
- Enzyme Inhibitors/pharmacology
- Glycerides/metabolism
- Lipoprotein Lipase/antagonists & inhibitors
- Lipoprotein Lipase/metabolism
- Male
- Mesenteric Arteries/drug effects
- Mesenteric Arteries/enzymology
- Mesenteric Arteries/metabolism
- Miconazole/pharmacology
- Peptides/pharmacology
- Phenylephrine/pharmacology
- Phospholipase A2 Inhibitors
- Phospholipases A2/metabolism
- Piperidines/pharmacology
- Potassium Channel Blockers/pharmacology
- Potassium Channels, Calcium-Activated/antagonists & inhibitors
- Potassium Channels, Calcium-Activated/metabolism
- Pyrazoles/pharmacology
- Quinacrine/pharmacology
- Rats
- Rats, Wistar
- Receptor, Cannabinoid, CB1/antagonists & inhibitors
- Receptor, Cannabinoid, CB1/metabolism
- Receptors, Calcium-Sensing/metabolism
- Rimonabant
- Signal Transduction/drug effects
- Vasoconstrictor Agents/pharmacology
- Vasodilation
- Vasodilator Agents/pharmacology
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