The cell potential of isolated inner hair cells in vitro

Inner hair cells (IHCs) were isolated from the 3rd and 4th turn of the guinea-pig cochlea using a new microsurgical technique. Microelectrode impalements in vitro with conventional microelectrodes yielded intracellular potentials of -14 +/- 7 mV (mean +/- SD, N = 43) at 24 degrees C. This suggested depletion of intracellular K+ in the isolated IHCs. Whole-cell recordings with patch-clamp suction electrodes of 11 +/- 3 M omega when filled with KCl Ringer demonstrated reloading of the cytoplasmic compartment with K+ (time constant t = 26.3 +/- 3.5 s), resulting in stable intracellular potentials after equilibration of -58.7 +/- 7.3 mV (mean +/- SD, N = 6) which is close to the K+ Nernst potential. The results suggest that IHC membranes are predominantly potassium-permeable. Assuming that in vivo the apical membranes of IHCs are exposed to endolymph-like fluid, the lower resting potentials of IHCs can be explained with the potassium permeability ratio of their apical and basolateral membranes. In whole-cell recordings, injection of hyperpolarizing current induced larger changes of the intracellular potential than depolarizing current. Oscillatory potential fluctuations were not observed, neither spontaneous nor in response to rectangular current pulses.