Phenothiazines and related compounds disrupt mitochondrial energy production by a calmodulin-independent reaction

Abstract

Phenothiazines and related compounds bind to mitochondrial membranes in approximate proportion to their affinities for calmodulin. Penfluridol (16 μM), pimozide (20 μM), or trifluoperazine (66 μM) completely inhibit ADP-stimulated respiration in isolated rat liver mitochondria, but exert no effect on either uncoupler- or Ca 2+-stimulated respiration. The inhibition of ADP-stimulated respiration results from inhibition of the oligomycin-sensitive ATPase. Inhibition of the ATPase does not involve interaction of phenothiazine with calmodulin. The addition of calmodulin with or without calcium to mitochondrial inner membrane preparations has no effect on ATPase activity. The addition of EGTA and the ionophore A23187 prior to the addition of phenothiazine does not prevent the phenothiazine-induced inhibition of the ATPase. Measurements of inner membrane calmodulin content by gel electrophoresis or cyclic nucleotide phosphodiesterase activation are negative. Despite the absence of calmodulin in the inner membrane preparations, 12.5 nmol trifluoperazine bind per 100 μg of membrane protein with an association constant, K, of 6.5 · 10 4 M −1. We conclude that calmodulin-binding neuroleptic agents, when added to whole cells, have the potential to disrupt mitochondrial energy production by a reaction which apparently does not involve a phenothiazine-calmodulin interaction.