108-pS Channel in Brown Fat Mitochondria Might Be Identical to the Inner Membrane Anion Channel

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.