MgATP-independent and MgATP-dependent exocytosis. Evidence that MgATP primes adrenal chromaffin cells to undergo exocytosis.
The MgATP dependency of secretion was investigated in digitonin-permeabilized adrenal chromaffin cells. Shortly after permeabilization there is a component of Ca2+-dependent secretion that occurs in the absence of MgATP in the medium. This secretion occurs from cells which are permeable to Ca2+/[ethylene-bis(oxyethylenenitrilo)]tetraacetic acid buffers, to nucleotides, and to proteins. It is prevented by treatment of cells with metabolic inhibitors to reduce cellular ATP prior to permeabilization. The rate of MgATP-independent secretion is rapid and terminates by approximately 2 min after introduction of Ca2+. MgATP-independent secretion is labile and is lost unless Ca2+ is introduced within 8 min of permeabilization. MgATP-dependent secretion occurs at a slower rate than MgATP-independent secretion and continues at a constant rate for 12 min. Preincubation of permeabilized cells with MgATP enhances Ca2+-dependent secretion during a subsequent incubation in the absence of MgATP. Similar MgATP sensitivities are observed when MgATP is present only prior to or only during stimulation with Ca2+ with half-maximal stimulation occurring at 0.4-0.5 and 0.6 mM MgATP, respectively. The data indicate that intact cells are primed by intracellular ATP so that immediately upon permeabilization, there is a component of secretion which is independent of medium MgATP. MgATP partially maintains the primed state after permeabilization by acting before Ca2+ in the secretory pathway.
Holz
R W
RW
Department of Pharmacology, University of Michigan Medical School, Ann Arbor 48109-0626.
Bittner
M A
MA
Peppers
S C
SC
Senter
R A
RA
Eberhard
D A
DA
D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D005089:Exocytosis / Q000187:drug effects*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism
D000255:Adenosine Triphosphate; D008274:Magnesium; D002118:Calcium; D009638:Norepinephrine