Ca2+-dependent K+ channels from rat olfactory cilia characterized in planar lipid bilayers

Olfactory cilia contain cyclic nucleotide-gated and Ca2+-dependent Cl− conductances that underlie excitatory chemotransduction, and a Ca2+-dependent K+ (KCa) conductance, apparently involved in inhibitory transduction. Previous single-channel patch-clamp studies on olfactory cilia revealed four different KCas, with different conductances and kinetics. Here, we further characterized these channels in planar bilayers, where blockers could be properly tested. All four ciliary KCas were observed: The 16 pS channel, K0.5,Ca = 40 μM and apamin-sensitive; the 30 and 50 pS channel, K0.5,Ca = 59 μM, clotrimazole-sensitive and charybdotoxin-insensitive; the 60 pS channel, clotrimazole-sensitive and charybdotoxin-insensitive; and the 210 pS channel, K0.5,Ca = 63 μM, blocked by charybdotoxin and iberiotoxin. The presence of the 16 and 210 pS channels was confirmed by immunoblotting.