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 cells (OHCs) from the guinea-pig cochlea. These sensory cells probably determine, via their motile activity, the fine tuning of sound frequencies and the high sensitivity of the inner ear. A Ca2+ -activated nonselective cationic channel was found in excised inside-out membrane patches. The current/voltage relationship was linear with a unit conductance 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 relative permeability of Na to C1); it was equally permeant to the Na+ and K+ ions and exhibited a low permeability to N-methyl-D-glucamine and 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 probability (P-o) was maximal at 10(-3) mol/l (P-o = 0.72+/-0.06, n = 12). 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, respectively, when they were added at a concentration of 10(-3) mol/l to the internal side. The channel was partially blocked by flufenamic acid (10(-4) mol/l) and 3',5'-dichlorodiphenylamine-2-carboxylic acid (DCDPC, 10(-5) mol/l). This type of channel, together with Ca2+ -activated K+ channels, might participate in the control of membrane potential and modulate the motility of OHCs.