BAPTA-AM blocks both voltage-gated and Ca2+-activated K+ currents in cultured bovine chromaffin cells

The effects of the membrane permeant Ca2+ chelator BAPTA-AM on voltage-gated Na+, Ca2+, K+ (I(Na), I(Ca) I(K), respectively) and Ca2+-activated K+ (I(KCa)) currents in cultured bovine chromaffin cells were investigated using the whole-cell patch-clamp technique. Superfusion with BAPTA-AM (50 microM) induced a rapid (< 60 s) and reversible block of both I(KCa) and I(K) (approximately 50%), without affecting either I(Ca) or I(Na). Preincubation with BAPTA-AM (50 microM, 30 min) or cell loading with the nonpermeable active form of BAPTA (10 mM in the pipette solution) permanently blocked I(KCa). BAPTA-AM superfusion (50 microM) also blocked I(K) (approximately 53%) after BAPTA-loading or BAPTA-AM preincubation. In conclusion, we show a fast and reversible block of I(KCa) and I(K) by BAPTA-AM, acting directly on K+ channels before it operates as a Ca2+ chelator, in cultured bovine chromaffin cells.