Proton electrochemical potential of the inner mitochondrial membrane in isolated perfused rat hearts, as measured by exogenous probes.

The membrane potential (delta psi) and delta pH of the inner mitochondrial membrane were studied in isolated perfused rat hearts using exogenous labelled probes and tissue fractionation in non-aqueous media. The mitochondrial delta psi, measured by means of the subcellular distribution of [3H]triphenylmethylphosphonium (TPMP+), was 125 +/- 7 mV (negative inside) in hearts beating at 5 Hz and 150 +/- 3 mV (negative inside) in hearts beating at 1.5 Hz. The mitochondrial membrane delta pH, measured by means of the subcellular distribution of low concentrations of [1-14C]propionate, was 0.63 +/- 0.06 pH units (alkaline inside) in hearts beating at 5 Hz and 0.53 +/- 0.12 pH units (alkaline inside) in hearts beating at 1.5 Hz. The implication of proton and electron gradients in the regulation of cellular respiration is discussed. In combination with previous evidence on adenylate distribution in the isolated perfused rat heart, the results indicate that the mitochondrial electrogenic adenylate translocator is in near equilibrium with delta psi.