Membrane responses to extracellular ATP in rat isolated white adipocytes.

We used whole-cell and perforated-patch voltage-clamp methods to study the membrane electrical properties of isolated rat epididymal and inguinal white adipocytes. We examined cells from both Sprague-Dawley and Zucker lean and Zucker obese (fa/fa) rats. A delayed-rectifier potassium current was present and similar in unstimulated white fat cells from all these sources. The potassium current activated rapidly with depolarization positive to about -30 mV and showed slow inactivation. Stimulation with extracellular ATP activated both hyperpolarizing and depolarizing conductances. ATP exposure also increased cell membrane capacitance by an average of 16%, suggesting that ATP activates exocytosis. Exposure to norepinephrine had little electrophysiological effect. We conclude that white adipocytes are very similar to brown adipocytes in their resting electrophysiological profile and in their responses to extracellular ATP.