Action of 2,3-butanedione monoxime on capacitance and electromotility of guinea-pig cochlear outer hair cells

1. Whole-cell patch-clamp recordings were obtained from isolated cochlear o uter hair cells (OHCs) while applying 2,3-butanedione monoxime (BDM) by pre ssure. BDM (5 mM) shifted the range of voltage sensitivity of membrane capa citance and cell length in the hyperpolarised direction by -49.6 +/- 4.0 mV (n = 12; mean +/- S.E.M.), without appreciable effects on membrane conduct ance. The shift was completely reversible and dose dependent, with a Hill c oefficient of 1.8 +/- 0.4 and a half-maximal dose of 3.0 +/- 0.8 mM (values +/- S.D). 2. The shift of the capacitance curve was also reproducible in cells whose natural turgor had been removed. BDM had no detectable effect on the capaci tance of Deiters' cells, a non-sensory cell type of the organ of Corti. 3. The effect of BDM on membrane capacitance was faster than that of salicy late. At similar saturating concentrations (20 mM), the time constant of th e capacitance changes was 1.8 +/- 0.3 s (n = 3) for salicylate and 0.75 +/- 0.06 s (n = 3) for BDM. The recovery periods were 13 +/- 1 s and 1.7 +/- 0 .4 s, respectively (means +/- S.E.M.). 4. The effect of BDM, a known inorganic phosphatase, was compared to the ef fects of okadaic acid, trifluoperazine and W-7, which are commonly used in studies of protein phosphorylation. Incubation of OHCs with okadaic acid (1 muM, 30-60 min) shifted the voltage sensitivity of the membrane capacitanc e in the hyperpolarised direction. Incubation with trifluoperazine (30 muM) and W-7 (150 muM) shifted it in the opposite, depolarised direction. BDM i nduced hyperpolarising shifts even in the presence of W-7. 5. Simultaneous measurement of membrane capacitance and intracellular free Ca2+ concentration ([Ca2+](i)) showed that BDM action on OHC voltage-depend ent capacitance and electromotility is not mediated by changes of [Ca2+](i) . 6. Our results suggest that: (a) the effects of BDM are unrelated to its in organic phosphatase properties, cell turgor conditions or Ca2+ release from intracellular stores; and (b) BDM may target directly the voltage sensor o f the OHC membrane motor protein.