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 Ca(2+)-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 (PNa/PCl = 18 where PNa/PCl denotes the relative permeability of Na to Cl); 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 (Po) was maximal at 10(-3) mol/l (Po = 0.72 +/- 0.06, n = 12). Adenosine 5'mono-, tri- and di-phosphate reduced Po to 29 +/- 14 (n = 5), 42 +/- 10 (n = 8) and 51 +/- 12 (n = 5) % of control Po, 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 Ca(2+)-activated K+ channels, might participate in the control of membrane potential and modulate the motility of OHCs.