K+ Channel Activity (k+ + channel_activity)

Distribution by Scientific Domains

Selected Abstracts

Xanthine-analog, KMUP-2, enhances cyclic GMP and K+ channel activities in rabbit aorta and corpus cavernosum with associated penile erection

Rong-Jyh Lin
Abstract The pharmacological properties of KMUP-2 were examined in isolated rabbit aorta and corpus cavernosum smooth muscle (CCSM). KMUP-2 caused relaxations that were attenuated by removed endothelium, high K+, and pretreatment with the soluble guanylate cyclase (sGC) inhibitors methylene blue (10 ,M) and ODQ (1 ,M), a NOS inhibitor, L-NAME (100 ,M), a K+ channel blocker TEA (10 mM), a KATP channel blocker glibenclamide (1 ,M), a voltage-dependent K+ channel blocker 4-AP (100 ,M), and the Ca2+ -dependent K+ channel blockers apamin (1 ,M) and charybdotoxin (ChTX, 0.1 ,M). The relaxant responses of KMUP-2 (0.01, 0.05, 0.1 ,M) together with a PDE inhibitor, IBMX (0.5 ,M), had additive effects on rabbit aorta and CCSM. Additionally, KMUP-2 (100 ,M) also affected cGMP metabolism, due to its inhibiting activity on PDE in human platelets. KMUP-2 (0.1,100 ,M) further induced an increase of intracellular cGMP levels in the primary cultured rabbit aortic and CCSM cells. These increases in cGMP content were abolished in the presence of methylene blue (100 ,M) and ODQ (10 ,M). Obviously, the relaxant effects of KMUP-2 on rabbit isolated tissues are more sensitive in CCSM than in aorta. Moreover, KMUP-2 also stimulated NO/sGC/cGMP pathway and subsequent elevation of cGMP by blockade of PDE and enhanced opening of K+ channels in rabbit aorta and CCSM. KMUP-2 (0.2, 0.4, 0.6 mg/kg), similar to KMUP-1 and sildenafil, caused increases of intracavernous pressure (ICP) and duration of tumescene (DT) in a dose-dependent manner. It is concluded that both the increases of cGMP and the opening activity of K+ channels play prominent roles in KMUP-2-induced aortic smooth muscle and CCSM relaxation and increases of ICP in rabbits. Drug Dev. Res. 55:162,172, 2002. 2002 Wiley-Liss, Inc. [source]

Calcium channel blockers inhibit galvanotaxis in human keratinocytes

Donna R. Trollinger
Directed migration of keratinocytes is essential for wound healing. The migration of human keratinocytes in vitro is strongly influenced by the presence of a physiological electric field and these cells migrate towards the negative pole of such a field (galvanotaxis). We have previously shown that the depletion of extracellular calcium blocks the directional migration of cultured human keratinocytes in an electric field (Fang et al., 1998; J Invest Dermatol 111:751,756). Here we further investigate the role of calcium influx on the directionality and migration speed of keratinocytes during electric field exposure with the use of Ca2+ channel blockers. A constant, physiological electric field strength of 100 mV/mm was imposed on the cultured cells for 1 h. To determine the role of calcium influx during galvanotaxis we tested the effects of the voltage-dependent cation channel blockers, verapamil and amiloride, as well as the inorganic Ca2+ channel blockers, Ni2+ and Gd3+ and the Ca2+ substitute, Sr2+, on the speed and directionality of keratinocyte migration during galvanotaxis. Neither amiloride (10 ,M) nor verapamil (10 ,M) had any effect on the galvanotaxis response. Therefore, calcium influx through amiloride-sensitive channels is not required for galvanotaxis, and membrane depolarization via K+ channel activity is also not required. In contrast, Sr2+ (5 mM), Ni2+ (1,5 mM), and Gd3+ (100 ,M) all significantly inhibit the directional migratory response to some degree. While Sr2+ strongly inhibits directed migration, the cells exhibit nearly normal migration speeds. These findings suggest that calcium influx through Ca2+ channels is required for directed migration of keratinocytes during galvanotaxis and that directional migration and migration speed are probably controlled by separate mechanisms. J. Cell. Physiol. 193: 1,9, 2002. 2002 Wiley-Liss, Inc. [source]

Apical SK potassium channels and Ca2+ -dependent anion secretion in endometrial epithelial cells

Melissa L. Palmer
Apical uridine triphosphate (UTP) stimulation was shown to increase short circuit current (Isc) in immortalized porcine endometrial gland epithelial monolayers. Pretreatment with the bee venom toxin apamin enhanced this response. Voltage-clamp experiments using amphotericin B-permeablized monolayers revealed that the apamin-sensitive current increased immediately after UTP stimulation and was K+ dependent. The current,voltage relationship was slightly inwardly rectifying with a reversal potential of ,52 2 mV, and the PK/PNa ratio was 14, indicating high selectivity for K+. Concentration,response relationships for apamin and dequalinium had IC50 values of 0.5 nm and 1.8 ,m, respectively, consistent with data previously reported for SK3 channels in excitable cells and hepatocytes. Treatment of monolayers with 50 ,m BAPTA-AM completely blocked the effects of UTP on K+ channel activation, indicating that the apamin-sensitive current was also Ca2+ dependent. Moreover, channel activation was blocked by calmidazolium (IC50= 5 ,m), suggesting a role for calmodulin in Ca2+ -dependent regulation of channel activity. RT-PCR experiments demonstrated expression of mRNA for the SK1 and SK3 channels, but not SK2 channels. Treatment of monolayers with 20 nm oestradiol-17, produced a 2-fold increase in SK3 mRNA, a 2-fold decrease in SK1 mRNA, but no change in GAPDH mRNA expression. This result correlated with a 2.5-fold increase in apamin-sensitive K+ channel activity in the apical membrane. We speculate that SK channels provide a mechanism for rapidly sensing changes in intracellular Ca2+ near the apical membrane, evoking immediate hyperpolarization necessary for increasing the driving force for anion efflux following P2Y receptor activation. [source]

Oxygen-sensing pathway for SK channels in the ovine adrenal medulla

Damien J Keating
SUMMARY 1.,The intracellular pathways that modulate the opening of oxygen-sensitive ion channels during periods of hypoxia are poorly understood. Different tissues appear to use either NADPH oxidase or a rotenone-sensitive mechanism as an oxygen sensor. The aim of the present study was to identify the oxygen-sensing pathway in the oxygen-sensitive sheep adrenal medullary chromaffin cell (AMCC). 2.,The whole-cell patch-clamp technique was used to measure K+ currents in dissociated adult ovine chromaffin cells as well as SK channel currents expressed in the H4IIE cell line. 3.,Diphenyliodonium, an inhibitor of NADPH oxidase, had no effect on the hypoxia-evoked closure of K+ channels in primary AMCC, whereas the mitochondrial inhibitor rotenone abolished the hypoxia-evoked response. Both these compounds significantly reduced K+ current amplitude under normoxic conditions. 4.,One possible mechanism through which the oxygen sensor may modulate K+ channel activity is by altering the redox state of the cell. In sheep AMCC, altering the redox state by the addition of H2O2 to the extracellular solution increased K+ conductance. 5.,The oxygen-sensitive K+ (Ko2) channels in sheep chromaffin cells are from the SK family and the whole-cell conductance of cells expressing mouse SK2 or SK3, but not human SK1, was increased by H2O2 and decreased by the reducing agent dithiothreitol. 6.,These studies show that, in sheep AMCC, Ko2 channels are modulated via a rotenone-sensitive mechanism and that alteration of the cellular redox state mimics the change produced by alterations in Po2. In a heterologous expression system, SK2 and SK3 channels, the channels that initiate hypoxia-evoked changes in AMCC function, are modulated appropriately by changes in cellular redox state. [source]