IDENTIFICATION OF ANION-SELECTIVE CHANNELS IN THE BASOLATERAL MEMBRANE OF MITOCHONDRIA-RICH EPITHELIAL-CELLS

Epithelial cells of toad (Bufo bufo) skin were isolated by treatments of the epidermis with collagenase and trypsin. Cl- channels in the bas olateral membrane from soma or neck of mitochondria-rich cells were st udied in cell-attached and excised inside-out configurations. Of a tot al of 87 sealed patches only 28 (32%) were electrically active, and in these we identified four different types of Cl- channels. The two maj or populations constituted Ohmic Cl- channels with limiting conductanc e (gamma(125/125)) Of 10 PS and 30 pS, respectively. A much rarer 150 pS Ohmic Cl- channel was also characterized. From i/V relationships of individual channels the following Goldman-Hodgkin-Katz permeabilities were calculated, 2.2 (+/-0.1) x 10(-14), 5.7 (+/-0.7) x 10(-14) and 3 2 (+/-2) x 10(-14) cm(3)/sec, for the 10, 30 and 150 pS Cl- channels, respectively. The 30 pS channel was activated by hyperpolarization. Th e gating kinetics of the 150 pS channel was complex with burstlike clo sures within openings of long duration. The fourth type of Cl- channel was studied in patches generating 'noisy currents' with no discrete s ingle-channel events, but with vanishing fluctuations at pipette poten tials near E-Cl. Noise analysis revealed a power spectrum with cutoff frequencies of 1.2 and 13 Hz, indicating that resolution of kinetic st eps was limited by small channel currents rather than fast channel gat ing. From the background noise level we estimated the channel conducta nce to be less than 1.7 pS. Despite the fact that the majority of patc hes did not contain electrically active Cl- channels.