The direct effects of alloxan in vitro on the handling of Ca2+ by microsomal fractions from dog aortic smooth muscle were investigated. Preincubation of the vascular-muscle microsomal membranes with alloxan showed a suppression of both binding of Ca2+ (in the absence of ATP) and ATP-driven Ca2+ transport. Alloxan substantially inhibited the microsomal ATP-driven Ca2+ transport stimulated by Pi, but not that stimulated by oxalate. Studies using subfractions isolated from the microsomal membranes on a sucrose density gradient indicated that plasma membrane is the primary site of action of alloxan on the ATP-driven Ca2+ transport.
