Correlated ATP-induced changes in membrane area and membrane conductance in single rat adipocytes

In the past few years it has been shown that, like many other non-neuroendocrine cells, adipocytes possess a mechanism for triggered exocytosis. Endocytosis and exocytosis affect the plasma membrane surface area, which can be directly monitored with electrophysiological patch-clamp techniques by measuring membrane capacitance, a parameter linearly related to the plasma membrane area. In this study we used the whole-cell mode of the patch-clamp technique to measure changes in membrane capacitance to monitor the effect of extracellular adenosine triphosphate (ATP) on the dynamics of membrane area changes in single adipocytes. Experimental evidence shows that extracellular application of ATP (100 mu M) increases membrane capacitance for 30 +/- 2%. In controls a significantly smaller increase of 3 2% was measured, which is due to a slow exocytic-endocytic membrane cycling rate of 0.3%/min. We found that ATP induces a transient increase in membrane current, temporally associated with the peak rate in membrane capacitance increase. These results show directly the presence of ATP-induced increase in membrane area correlated to the increase in membrane current in single adipocytes.