Electrolyte-activated lipolysis in vitro: Modifying effect of calcium

In vitro experiments, employing rat epididymal fat tissue, have shown spontaneous lipolysis to be induced by Cafree media containing high K concentrations. Electrolyte-activated lipolysis proceeds linearly over a 2 hour incubation period and is not affected by omission of albumin from incubation media. Inclusion of 2.5 mEq./L. Ca in the medium sensitizes adipose tissue to low concentrations of K but results in a biphasic response, wherein lipolysis in all-K media is less than in mixed Na/K media. Neither Mg nor buffer anions were found to play any role in the response, except that in all-PO 4 buffers lipolysis developed at lower K concentrations than in Ca-free Cl-HCO 3 buffers; a similar effect was achieved by adding EDTA to Cl-HCO 3 buffer. Cysteine did not modify the response to Ca. Although the response to Na/K buffers in the presence of Ca is not specific, in that similar effects were achieved in mixed Na/choline buffers, extrapolation to the in vivo state suggests that Na/K flux may play a role in regulating the basal state of adipose tissue, in modifying the capacity to respond to lipolytic stimuli, and serve in orienting the tissue in generally anabolic or catabolic directions.