Millisecond studies of secretion in single rat pituitary cells stimulated by flash photolysis of caged Ca2+.
To study the final steps in the secretory pathway of rat pituitary melanotrophs, we have monitored changes in cell surface area due to exocytosis after flash photolysis of caged Ca2+. A step increase in cytosolic [Ca2+] to 45-125 microM triggers three phases of exocytic secretion. A small cohort of a few hundred vesicles is exocytosed in 40 ms in a secretory burst with a peak rate of 17,000 vesicles/s. Next, 2700 more vesicles are released in a slower phase that is complete within 400-1000 ms. Finally, vesicles continue to be released slowly (500 vesicles/s) for > 8s. The approach described provides a way to identify and monitor the final steps in the secretory pathway at millisecond resolution. That a small portion of secretory vesicles can be released much faster than all others suggests that these vesicles are functionally equivalent to those at the presynaptic active zone of a neuron. Their release would be fast enough to be temporally correlated with single action potentials.
Thomas
P
P
Department of Physiology and Biophysics, University of Washington, Seattle 98195.
Wong
J G
JG
Almers
W
W
D000085:Acetates; D000818:Animals; D002462:Cell Membrane / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D005029:Ethylenediamines; D005089:Exocytosis; D016257:Fura-2; D007700:Kinetics; D008564:Membrane Potentials; D010782:Photolysis; D010902:Pituitary Gland / Q000378:metabolism*; D051381:Rats; D013050:Spectrometry, Fluorescence; D013997:Time Factors
D000085:Acetates; D002614:Chelating Agents; D005029:Ethylenediamines; C057014:DM-nitrophen; D016257:Fura-2