Promotion of lipolysis in rat adipocytes by pertussis toxin: reversal of endogenous inhibition

Pertussis toxin (PT), a protein produced by Bordetella pertussis, was studied for its effect on lipolysis in isolated rat epididymal adipocytes. Exposure of adipocytes to pertussis toxin resulted in a significant increase in cyclic AMP levels and lipolysis after a lag of 1-2 hr. Both the maximal rate of lipolysis and the time lag (beyond 1 hr) were PT concentration-dependent. Heat treatment (95 degrees C, 30 min) or incubation with specific antibody directed against PT eliminated the ability of toxin to increase lipolysis. Cell-free culture medium from B. pertussis, but not from nontoxigenic Bordetella species, had the same effect on lipolysis as purified toxin. Comparison of the PT effect with the known lipolytic effect of cholera toxin (CT) revealed that the two toxins elicited responses that were indistinguishable in time course and magnitude. In contrast, the adenylate cyclase (EC 4.6.1.1) activities in membranes prepared from PT- or CT-treated adipocytes were different. Adenylate cyclase activity in membranes from control (untreated) adipocytes was inhibited 35-64% by the adenosine analogue N6-(L-2-phenylisopropyl)-adenosine. As expected from previous studies, membranes from CT-treated adipocytes demonstrated an increased basal activity but showed the same proportional inhibition by N6-(L-2-phenylisopropyl)-adenosine as controls. On the other hand, membranes from adipocytes exposed to PT (400 ng/ml for 4 hr) showed no increase in basal adenylate cyclase activity but had reduced sensitivity to N6-(L-2-phenylisopropyl)-adenosine inhibition, with the maximal effect ranging from 11 to 30% at 10(-6) M N6-(L-2-phenylisopropyl)-adenosine. These data support the hypothesis that PT promotes cyclic AMP-dependent lipolysis in a manner quantitatively equivalent to CT, but by a different mechanism involving increased cyclic AMP levels resulting from loss of responsiveness to endogenous inhibitors such as adenosine.