Direct measurement of exocytosis and calcium currents in single vertebrate nerve terminals.
The release of neurohormone is widely thought to be exocytotic, involving Ca2(+)-dependent fusion of secretory vesicles with the plasma membrane. The inaccessibility of most nerve ending 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 capacitance, we have now monitored changes in the surface membrane area of individual nerve terminals isolated from the mammalian neurohypophysis. A single depolarizing pulse leading to Ca2+ entry through voltage-gated calcium channels, 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, fatigue and recovery of the release process.
Lim
N F
NF
Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104.
Nowycky
M C
MC
Bookman
R J
RJ
D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000502:physiology*; D003594:Cytoplasmic Granules / Q000502:physiology; D004533:Egtazic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D005089:Exocytosis; D009411:Nerve Endings / Q000502:physiology*; D010904:Pituitary Gland, Posterior / Q000502:physiology
D015220:Calcium Channels; D004533:Egtazic Acid; D002118:Calcium