BACTERIAL-ENDOTOXIN ALTERS KINETICS OF BK CHANNELS IN RAT CEREBROVASCULAR SMOOTH-MUSCLE CELLS

Patch-clamp recordings were used to study the effects of Escherichia c oli bacterial endotoxin (lipopolysaccharide, LPS) on the properties of large-conductance, Ca2+-dependent K+ channels (BK channels) in the me mbrane of enzymatically dispersed rat cerebrovascular smooth muscle ce lls (CVSMCs). LPS had negligible effects on the kinetic and conductanc e properties of BK channels when applied to the extracellular domain o f these channels. However, acute application of LPS (10-100 mu g/ml) t o inside-out patches of CVSMC membrane isolated in a cell-free environ ment rapidly and reversibly increased the open probability of BK chann els, leaving the conductance of these channels unaltered, The magnitud e of this effect decreased as the concentration of free Ca2+ at the cy toplasmic membrane face was lowered, but was little affected by change s in membrane potential. Kinetic analysis showed that LPS accelerated reopening of BK channels while having little effect on mean channel op en time. Detoxified E. coli LPS, from which the fatty acid chains of L ipid A were partially removed, showed slightly reduced activity when c ompared to the parent endotoxin molecule. A purified E. coli Lipid A h ad negligible effects on BK channel function. These results indicate t hat LPS activates BK channels in cerebrovascular smooth muscle cells w hen present at the cytoplasmic membrane face. This novel mechanism may provide insights into the regulation of BK channels by intracellular, membrane-associated elements. (C) 1998 Elsevier Science B.V.