Membrane potential of rat adipocytes: Effect of phospholipase C, concanavalin A, and adenosine

The change in transmembrane potential of rat adipocytes was measured using the fluorescent probe 3,3'-diethylthiadicarbocyanine iodide, diS-C₂-(5). The method was calibrated by altering the potassium ion concentration while keeping the sum of potassium and sodium ions at a constant concentration of 153 mM (Bailey et al: Bioelectrochem. Bioenergetics 21:333-42. 1989). Two insulin-mimetic agents, phospholipase C from Clostridium perfringens and concanavalin A, induced a dose dependent hyperpolarization of rat epididymal adipocytes, like insulin. Removal of endogenous adenosine with adenosine deaminase or adenosine receptor blockade with isobutylmethylxanthine following the initiation of insulin-induced hyperpolarization resulted in depolarization. These same agents induced hyperpolarization of -6 to -8 mV when added without insulin. The replacement of adenosine with its analogue, N⁶-phenylisopropyladenosine, plus insulin depolarized the cells toward the transmembrane potential established by insulin, -2.0 mV. These studies suggest that adenosine receptor occupancy is required to maintain insulin- induced hyperpolarization.