Single-channel and whole-mitoplast patch-clamp recordings were employed to characterize the 108-pS (Cl-) channel in brown fat mitochondrial mitoplasts. We demonstrated the ability of this channel to conduct di- and trivalent anions, such as sulfate, phosphate, and benzenetricarboxylates, and its blockage by propranolol, 1,4-dihydropyridine-type Ca2+ antagonists, and Cibacron blue. Moreover, we have revealed its pH dependence for the first time. As a basis for the characteristic potential dependence of the whole-mitoplast current, we identified an open probability, increasing with depolarizing (positive) potentials, Eh, and being almost zero in the hyperpolarizing range. Events at negative Eh exhibit a short flickering behavior, whereas at positive Eh, they become much longer. This voltage dependence is influenced by pH in such a way that, at acidic pH, the 108-pS channel possesses a low open probability throughout the observed potential range, whereas at alkaline pH, the channel switches to long openings, even at a negative potential. All these properties lead us to conclude that the inner membrane anion channel, which has been characterized only by light scattering studies, and the 108-pS inner membrane channel, which has been characterized electrophysiologically, are one and the same process.

Department of Membrane Transport Biophysics Institute of Physiology Academy of Sciences of Czech Republic CZ 14220 Prague 4 Czech Republic

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