CHLORIDE CURRENTS OF SINGLE MITOCHONDRIA-RICH CELLS OF TOAD SKIN EPITHELIUM

1. Mitochondria-rich (MR) cells in free suspension were obtained by co llagenase and trypsin treatments of toad skin epithelium and studied b y whole-cell voltage clamp and membrane current fluctuation analysis. 2. Cells studied with a 100 mu M amiloride and 5 mM Ba2+ Ringer soluti on on the outside and 10 mM Cs+ in the pipette generated large membran e currents with reversal potentials varying in a Nernstian way with pi pette [Cl-]. 3. The membrane chloride currents were activated in exces s of Goldman-Hodgkin-Katz rectification by cell depolarization and cla mping to positive cell potentials (V-C) The resulting Cl- permeability was presented as an S-shaped function of membrane potential with half -maximal activation in the range 0 mV < V-C < 50 mV. 4. The power dens ity spectrum of Cl- current fluctuations could be fitted with a single Lorentzian component with a corner frequency, f(c), of 34.9 +/- 2.6 H z, and a low frequency asymptote, S-o, of 14.6 +/- 1.3 pA(2) s per cel l (mean +/- S.E.M.; V-C = 25 mV, E(Cl) = 0 mV, n = 6). 5. The lower-li mit single channel conductance, gamma(Cl)(1 - P-o), was 128 +/- 9 pS ( V-C = 25 mV, n = 6), where P-o is the open channel probability. With P -o = 0 5, this result indicates that Cl- channels of large unitary con ductance (200-300 pS) are present in the mitochondria-rich cell membra ne.