A temperature-sensitive step in exocytosis.
We have examined the temperature sensitivity of exocytosis in digitonin-permeabilized chromaffin cells. The time course of secretion is markedly slowed by incubating the cells at 18 degrees C rather than 27 degrees C. We have previously shown that secretion has both ATP-dependent and ATP-independent components (Holz, R. W., Bittner, M. A., Peppers, S. C., Senter, R. A., and Eberhard, D. A. (1989) J. Biol. Chem. 264, 5412-5419). Reducing the temperature has no effect on ATP-independent secretion. However, cold (18 degrees C) greatly slows the ability of ATP to stimulate secretion. The ATP-requiring priming step itself is not affected by reducing the temperature since an effect of ATP can be seen after permeabilization at 18 degrees C if the cells are subsequently stimulated to secrete at 27 degrees C. When cells are permeabilized at 27 degrees C with ATP and then stimulated by Ca2+ in the absence of ATP, the secretion which was primed by ATP during the permeabilization step is inhibited 75% at 18 degrees C. Similar results are seen when ATP-dependent priming is enhanced by low concentrations of Ca2+. Thus, the temperature-sensitive step occurs after ATP and Ca2+ act to prime the cell. The temperature-sensitive step is likely to be overall rate-limiting step during the later phase of secretion, when the ATP-dependent priming process is limiting.
Bittner
M A
MA
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0626.
Holz
R W
RW
D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D004072:Digitonin / Q000494:pharmacology; D005089:Exocytosis; D007700:Kinetics; D009638:Norepinephrine / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
D000255:Adenosine Triphosphate; D004072:Digitonin; D009638:Norepinephrine