Effects of potassium channel blockers on the acetylcholine-induced currents in dissociated outer hair cells of guinea pig cochlea

Much physiological evidence is available to show that acetylcholine (ACh) hyperpolarizes the outer hair cells (OHCs) of guinea pig cochlea and induces Ca2+-activated K+ currents. In this study, using the nystatin perforated patch-clamp technique, we investigated the effects of various K+ channel blockers on the ACh-induced currents (I-ACh) in dissociated OHCs of guinea pig cochlea. The I-ACh were inhibited by apamin in a concentration-dependent manner. The half-maximal inhibitory concentration for apamin on the ACh-induced response was 1.59 x 10(-9) M. Charybdotoxin and iberiotoxin had no inhibitory effect on the I-ACh. The inhibitory potency of the various K+ channel blockers on the I-ACh was as follows: apamin much greater than quinine approximate to quinidine approximate to d-tubocurarine > tetraethylammonium chloride > 4-aminopyridine approximate to Ba2+ > Cs2+. If is proposed that the Ca2+-activated K+ channels of mammalian cochlear OHCs should be classified as small conductance Ca2+-activated K+ (SK) channels according to their pharmacological properties. (C) 1997 Elsevier Science Ireland Ltd.