Effects of trypsin on large-conductance Ca(2+)-activated K(+) channels of guinea-pig outer hair cells

High-conductance Ca(2+)-activated K(+) (BK(Ca)) channels from isolated adult guinea-pig outer hair cells were studied in inside-out membrane patches. They had a 300 pS unitary conductance and were inhibited by tetraethyl ammonium (1 mM), iberiotoxin (33 nM) and charybdotoxin (50 nM). In symmetrical 144 mM KCl their K(+) permeability (P(K)) was 5.4 x 10(-13) cm(3)/s; this was reduced to around 4.5 x 10(-13) cm(3)/s with 160 mM Na(+) in place of K(+) on either internal or external membrane surface. BK(Ca) channels from trypsin-isolated hair cells had a high open probability, that depended on both membrane voltage (16 mV/e-fold change) and the concentration of calcium ions at their intracellular surface ([Ca(2+)](i)). The Hill coefficient was 3-4. About 50% of BK(Ca) channels from mechanically isolated outer hair cells had similar characteristics; the remainder had the same high conductance but a low open probability. Trypsin (