The role of calcium in insulin action. III. Calcium distribution in fat cells; its kinetics and the effects of adrenaline, insulin and procaine-HCl.

The effects of adrenaline, insulin and procaine-HCl on Ca distribution in intact fat cells and on Ca binding to fat cell ghost membranes have been investigated. 1. Fat cells incubated in 45Ca containing media till isotopic equilibrium indicated that the exchangeable Ca in these cells averages 25.7 +/-3.2nmol/mg protein, which represents approximately 9.8% of their ttotal Ca content. 2. Perifusion of 45Ca prelabelled fat cells gave washout curves whose analysis conformed with three kinetically distinct Ca pools (Fig. 1). The fast exchangeable pool (Compartment A) had an efflux rate constant of 0.193 +/-0. 013 min.-. The release of Ca from the second and thrid pools (Compartments B and C) was much slower with efflux rate constants of 0.032 +/-0.0018 min.-1 and 0.0042 +/- 0.0006 min.-1 respectively. Changing the Ca concentration in the perifusing medium modified the initial fast phase and its rate constant, while added dinitrophenol (DNP) inhibited the efflux rate from the later compartments...