Author:

Keywords:

Animals, Base Sequence, Calcium, Cells, Cultured, DNA Primers, DNA, Complementary, Endothelium, Vascular, Humans, In Vitro, Patch-Clamp Techniques, Potassium Channels, Research Support, Non-U.S. Gov't, Swine, Transfection, Science & Technology, Life Sciences & Biomedicine, Biochemistry & Molecular Biology, Biology, Cell Biology, Life Sciences & Biomedicine - Other Topics, endothelium, Slo, maxi K, channel subunit, patch-clamp, beta subunit expression, ACTIVATED POTASSIUM CHANNELS, SMOOTH-MUSCLE CELLS, LARGE-CONDUCTANCE, ION CHANNELS, VASCULAR ENDOTHELIUM, NONSELECTIVE CATION, MESENTERIC-ARTERY, HYPERTENSIVE RATS, HUMAN BRAIN, EXPRESSION, In Vitro Techniques, 0601 Biochemistry and Cell Biology, 0606 Physiology, 1116 Medical Physiology, 3101 Biochemistry and cell biology, 3208 Medical physiology

Abstract:

Hyperpolarizing large-conductance, Ca(2+)-activated K(+) channels (BK) are important modulators of vascular smooth muscle and endothelial cell function. In vascular smooth muscle cells, BK are composed of pore-forming alpha subunits and modulatory beta subunits. However, expression, composition, and function of BK subunits in endothelium have not been studied so far. In patch-clamp experiments we identified BK (283 pS) in intact endothelium of porcine aortic tissue slices. The BK opener DHS-I (0.05-0.3 micromol/l), stimulating BK activity only in the presence of beta subunits, had no effect on BK in endothelium whereas the alpha subunit selective BK opener NS1619 (20 micromol/l) markedly increased channel activity. Correspondingly, mRNA expression of the beta subunit was undetectable in endothelium, whereas alpha subunit expression was demonstrated. To investigate the functional role of beta subunits, we transfected the beta subunit into a human endothelial cell line (EA.hy 926). beta subunit expression resulted in an increased Ca(2+) sensitivity of BK activity: the potential of half-maximal activation (V(1/2)) shifted from 73.4 mV to 49.6 mV at 1 micromol/l [Ca(2+)](i) and an decrease of the EC(50) value for [Ca(2+)](i) by 1 microM at +60 mV was observed. This study demonstrates that BK channels in endothelium are composed of alpha subunits without association to beta subunits. The lack of the beta subunit indicates a substantially different channel regulation in endothelial cells compared to vascular smooth muscle cells.