Evidence for the electrogenic nature of the ATP-ADP exchange system in rat liver mitochondria

Abstract

A transient decrease in the fluorescent intensity of the dye, 3,3′-dipropylthiodicarbocyanine iodide was seen upon the addition of ATP to rat liver mitochondria which had been pre-treated with 2 · 10 −6 M rotenone and 3.3 μg oligomycin/ml. This decrease which is indicative of a hyperpolarization (internal more negative) was half maximal at 2 · 10 −5 M ATP and was not seen with either ADP or AMP. Atractyloside, bongkrekic acid, ADP and to a lesser extent AMP inhibited the decrease observed with ATP. The characteristics of inhibition by these compounds were similar to those observed in experiments where either transport or binding of adenine nucleotides was measured. The addition of ADP after ATP led to a transient increase in fluorescent intensity indicative of depolarization. This increase was also blocked by atractyloside and bongkrekic acid. The evidence presented supports the hypothesis that the exchange of ADP and ATP via an adenine nucleotide exchange mechanism is electrogenic.