Div. of Animal Physiology, Univ. Salzburg, Austria

Maxi calcium-activated potassium (BK) channels are one of the key targets of ethanol action. In GH4/C1 cells two BK channel splice variants are expressed (BK & BKstrex, carrying the ancillary strex-sequence). In this study an activating effect of 30 mM EtOH on BK channels in GH4/C1 pituitary tumor cells was found in outside-out patch clamp experiments. Enhanced BKstrex expression occurs under circumstances of high stress. BKstrex is more strongly activated (165 ± 32%, n=7) by EtOH than BK (148±14%, n=8). This argues for a stress-dependent impact of EtOH on BK channels. The underlying mechanisms leading to the stronger EtOH-induced BKstrex activation were investigated using cPKA and blockers of PKA, PKC, PP-1 and PP-2A. The involvement of different intracellular signalling molecules in the EtOH effect on the two BK channel splice variants was found. Furthermore extracellular application of 30 mM EtOH was shown to induce a significant increase in intracellular calcium (Cai; 121±2%, n=6), which can in part be ascribed to cellular calcium entry from the extracellular side, as omission of extracellular calcium resulted in a lower EtOH-induced rise in Cai (110 ± 1, n=6). This effect could contribute to BK channel activation by EtOH in GH4/C1 cells.