A remark on the high-conductance calcium-activated potassium channel in human endothelial cells

Abstract

The patch-clamp technique was used to examine the presence of large conductance calcium-activated potassium channels (BK_Ca) in human endothelial cells and to characterize their properties in terms of voltage dependence, ion conduction and blockade by iberiotoxin (IbTX). Experiments were performed using cell-attached and outside-out configurations on human umbilical vein endothelial cells (HUVEC). For the experiments HUVECs, which were passaged 6–19 times, were used. In early passages channel activities were absent suggesting the appearance of BK_Ca depending on cell culture time. The inverse logarithmic voltage sensitivity was 10.17 mV (median) for cell-attached recordings and 12.10 mV (median) for outside-out patches (membrane voltage range: 60–120 mV, symmetrical 140 mM K⁺ solutions). The I/V relationship was quasilinear in the range of 0–80 mV and exhibited a nonlinear behaviour under further depolarization suggesting some kind of saturation mechanism. Using a sigmoid function to fit the data, channel conductance was calculated as 172.9 pS (median) for cell-attached patches and as 262.1 pS (median) for outside-out patches. IbTX, known as one of the most selective blockers of BK_Ca was perfused to outside-out patches. In two out of three experiments there was complete block of the ion channel after 1 min.