979-35 Factors of Acute Ischemia Increase Ca2+-Activated K+ Currents in Cultured Human Endothelial Cells

Abstract

Ca 2+ -activated K + channels (K Ca ) in endothelial cells and their response to some pharmacological agents are well known. However, the regulative function of these channels on transmembrane potential under ischemic conditions is still obscure. Therefore, we examine the effects of some ischemic factors on K Ca channels in cultured human umbilical vein endothelial cells (HUVEC) by means of the patch-clamp technique. In whole-cell recordings (test potentials: -60 mV to ± 100 mV) the perfusion with an artificial (“ischemic”) Tyrode solution (pH = 6.8; pO 2 = 45 mmHg, glucose-free) of HUVEC caused a significant increase of an outward current in the voltage range of +40 mV to ± 100 mV (P < 0.05; n = 15; Fig. 1: I/V-relationship, mean values; Fig. 2: sample of recordings). These currents were completely blOCked by extracellular tetraethylammonium (TEA: 0.5 mM). whereas glibenclamide (10 μM) had no effect. In cell-attached patches (140 mM K + pipette solution) K Ca channels were characterized by their typical voltage dependence, their block by TEA and a single-channel slope conduction of 215 pS (±5.17 pS; n < 10). Superfusion of HUVEC with the artificial solution caused a significant increase in the open-state probability NP o (N: channels in the patch) of K Ca channels from 0.0141 ± 0.0056 to 0.0377 ± 0.0119 at +80 mV (p < 0.05: n = 6) and 0.0645 ± 0.0221 to 0.1599 ± 0.0485 at+100 mV (p < 0.05; n = 7)(Fig. 3: sample of K Ca recordings). Single channel conductance was not found to be changed. We conclude that the K Ca channel in endothelial cells is influenced by basic ischemic factors and may, under pathophysiological conditions, be of importance in regulating Ca 2+ -entry and stimulation-secretion coupling by modulating membrane potential.