A rapid phosphate-induced depression of heart subsarcolemmal mitochondrial oxidative phosphorylation

Inorganic phosphate (Pi) was added to suspensions of interfibrillar (IFM) and subsarcolemmal (SLM) mitochondria. With 20 mM Pi, significant depression in SLM oxidative phosphorylation was seen after 60 seconds exposure whereas 120 seconds was required to depress IFM, although to a lesser degree. Oxidative phosphorylation rate of SLM was significantly depressed by 1 minute incubation with 2.5-20 mM Pi, whereas IFM were unaffected. Five minute incubation with similar Pi concentrations produced equal depression in both populations. We postulate that the rapid increase in intracellular Pi may contribute to contractile failure associated with early ischemia by depressing a critical pool of ATP synthesis represented by SLM.