The regulation of ATPase-ATPase interactions in sarcoplasmic reticulum membrane. II. The influence of membrane potential.

Na3VO4 promotes the crystallization of Ca2+-ATPase in sarcoplasmic reticulum vesicles. The rate of vanadate-induced crystallization is dramatically increased by inside positive membrane potential generated through ion substitution. Negative potential caused the transient disruption of preformed Ca2+-ATPase crystals, followed by slower reappearance of the lattice after the potential was dissipated. We propose that positive transmembrane potential alters the conformation of the Ca2+-ATPase molecules in a manner that favors ATPase-ATPase interactions, while negative potential would have the opposite effect. Changes in enzyme conformation caused by potential changes during the contraction-relaxation cycle could regulate ATPase interactions in a similar manner in vivo, with effects upon the Ca2+ transport activity and permeability of the sarcoplasmic reticulum.