A REMARK ON THE HIGH-CONDUCTANCE CALCIUM-ACTIVATED POTASSIUM CHANNEL IN HUMAN ENDOTHELIAL-CELLS

The patch-clamp technique was used to examine the presence of large co nductance calcium-activated potassium channels (BKCa) in human endothe lial cells and to characterize their properties in terms of voltage de pendence, ion conduction and blockade by iberiotoxin (IbTX). Experimen ts were performed using cell-attached and outside-out configurations o n human umbilical vein endothelial cells (HUVEC). For the experiments HUVECs, which were passaged 6-19 times, were used. In early passages c hannel activities were absent suggesting the appearance of BKCa depend ing on cell culture time. The inverse logarithmic voltage sensitivity was 10.17 mV (median) for cell-attached recordings and 12.10 mV (media n) for outside-out patches (membrane voltage range: 60-120 mV, symmetr ical 140 mM K+ solutions). The I/V relationship was quasilinear in the range of 0-80 mV and exhibited a nonlinear behaviour under further de polarization. suggesting some kind of saturation mechanism. Using a si gmoid function to fit the data, channel conductance was calculated as 172.9 pS (median) for cell-attached patches and as 262.1 pS (median) f or outside-out patches. IbTX, known as one of the most selective block ers of BKCa was perfused to outside-out patches. In two out of three e xperiments there was complete block of the ion channel after 1 min.