2 TYPES OF CALCIUM CHANNELS IN BULLFROG SACCULAR HAIR-CELLS

Ca2+ channels were studied in cell-attached recordings from the basola teral membrane of the bullforg saccular hair cells with the EPC-9 patc h-clamp system. Pipettes contained 110 mM Ba2+ and the membrane potent ial was zeroed with isotonic potassium aspartate. Data acquisition and analysis were performed using E9SCREEN and M2LAB software. L-type cha nnel was distinguished by a single-channel conductance of 26 pS, activ ation range between -10 and +40 mV and intense activity even at a hold ing potential of -40 mV. The L-type channel showed characteristic burs ts of brief openings (mode 1) interrupted occasionally by longer openi ngs (mode 2). Bay K 8644 promoted the mode 2 activity and nifedipine i nhibited L-type channel activity. Another type of calcium channels, 20 pS channel, was detected by -50 to +10 mV depolarizing steps from a h olding potential of -40 or -80 mV. This channel was insensitive to dih ydropyridines and resembled the N-type channel.