STUDIES ON SIGNAL-TRANSDUCTION MECHANISMS FOR ADRENALINE-DRIVEN LIPOLYSIS IN WHITE AND BROWN ADIPOCYTES

White and brown rat adipocytes have been permeabilised by repeated exp osure of the cells in suspension to high voltage electrical discharges . The resulting preparations were permeable to low molecular weight ma terials, e.g., cyclic AMP, propidium iodide, and were stable in suspen sion with little evidence of rapid resealing, or of gross damage to th e cell membrane. Leakage of lactate dehydrogenase was not markedly enh anced except at voltages in excess of 2 kV cm(-1) for brown adipocytes . Exogenously-added cyclic AMP stimulated lipolysis (measured as glyce rol release) in the electropermeabilised adipocytes far more effective ly than in intact adipocytes. In brown, but not in white, adipocytes t his effect was enhanced by addition of millimolar ATP. The EC(50) for stimulation of glycerol release by cyclic AMP was 0.2 mu M in electrop ermeabilised brown adipocytes, and 2 mu M and 40 mu M in electropermea bilised white adipocytes obtained from weanling and adult rats respect ively. The effect of cyclic AMP on lipolysis was enhanced by addition of an inhibitor of cyclic AMP phosphodiesterases and was reduced by ad dition of 5'-AMP, adenosine or inosine (in brown adipocytes). Addition of adenosine deaminase caused a small, but significant, enhancement o f cyclic AMP-driven lipolysis. Catecholamine-driven lipolysis was obse rved in electropermeabilised brown and white adipocytes, especially in the presence of GTP. Adrenaline-, and to a lesser extent cyclic AMP-, driven lipolysis in electropermeabilised white adipocytes was inhibit ed by insulin. This effect of insulin was not enhanced by addition of GTP or of a metabolically stable GTP analogue. The results obtained es tablish the electropermeabilised preparation as suitable for analysis of signal transduction pathways in white and brown adipocytes.