Mechanically and ATP-induced currents of mouse outer hair cells are independent and differentially blocked by d-tubocurarine

Mechano-electrical transducer channels (MET) and ATP-gated ion channels (P2X receptors) of hair cells have several properties in common: they share the same location at the apex of the cell, both channels are non-selective for cations and blocked by aminoglycosides and pyrazinecarboxamides (amiloride-related compounds). In this study, we test the relationship and possible identity of these two channel types. Using whole-cell patch-clamp recordings of outer hair cells (OHCs) of the cultured neonatal mouse cochlea and a fluid jet to stimulate their hair bundles mechanically, we show that d-tubocurarine, a blocker of P2X(2) receptors, blocks MET channels with a half-blocking concentration of 2.3 mu M. In contrast, the K-D for the P2X(2) receptors was 90 mu M and 84 mu M measured in hair cells and Xenopus oocytes, respectively. When hair bundles of OHCs were simultaneously stimulated with saturating mechanical stimuli and superfused by 100-300 mu M ATP, transducer currents and ATP-activated currents were elicited simultaneously. Their amplitudes were additive, however. We conclude that MET-and ATP-activated currents are mediated by two distinct channel populations in hair cells. (C) 1997 Elsevier Science Ltd.