A CALCIUM-ACTIVATED NONSELECTIVE CATIONIC CHANNEL IN THE BASOLATERAL MEMBRANE OF OUTER HAIR-CELLS OF THE GUINEA-PIG COCHLEA

The patch-clamp technique was used to investigate ion channels in the basolateral perilymph-facing membrane of freshly isolated outer hair c ells (OHCs) from the guinea-pig cochlea. These sensory cells probably determine, via their motile activity, the fine tuning of sound frequen cies and the high sensitivity of the inner ear. A Ca2+ -activated nons elective cationic channel was found in excised inside-out membrane pat ches. The current/voltage relationship was linear with a unit conducta nce of 26.3+/-0.3 pS (n = 15) under symmetrical inger conditions. The channel excluded anions (P-Na/P-C1 = 18 where P-Na/P-C1 denotes the re lative permeability of Na to C1); it was equally permeant to the Na+ a nd K+ ions and exhibited a low permeability to N-methyl-D-glucamine an d Ba2+ or Ca2+. Channel opening required a free Ca2+ concentration of about 10(-6) mol/l on the internal side of the membrane and the open p robability (P-o) was maximal at 10(-3) mol/l (P-o = 0.72+/-0.06, n = 1 2). Adenosine 5'mono-, tri- and di-phosphate reduced P-o to 29+/-14 (n = 5), 42+/-10 (n = 8) and 51+/-12 (n = 5) % of control P-o, respectiv ely, when they were added at a concentration of 10(-3) mol/l to the in ternal side. The channel was partially blocked by flufenamic acid (10( -4) mol/l) and 3',5'-dichlorodiphenylamine-2-carboxylic acid (DCDPC, 1 0(-5) mol/l). This type of channel, together with Ca2+ -activated K+ c hannels, might participate in the control of membrane potential and mo dulate the motility of OHCs.