THE release of neurohormone is widely thought to be exocytotic, involving Ca2+-dependent1,2 fusion of secretory vesicles3,4 with the plasma membrane5. The inaccessibility of most nerve endings has so far hampered direct time-resolved measurements of neuronal exocytosis in response to brief depolarization. By using 'whole-terminal' patch-clamp and circuit-analysis techniques to measure membrane capacitance6, we have now monitored changes in the surface membrane area of individual nerve terminals isolated from the mammalian neurohypophysis7. A single depolarizing pulse leading to Ca2+ entry through voltage-gated calcium channels8, rapidly and reproducibly increases the membrane area by an amount corresponding to the fusion of 1-100 secretory vesicles. The magnitude of the capacitance increase depends not only on Ca2+ entry and buffering, but also on the pattern of stimulation revealing facilitation, fatieue and recovery of the release process.
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