Multiple calcium pathways induce the expression of SNAP-25 protein in chromaffin cells.
Incubation of bovine adrenal chromaffin cells in high K+ (38 mM) during 24-48 h enhanced 2.5 to five times the expression of SNAP-25 protein and mRNA, respectively. This increase was reduced 86% by furnidipine (an L-type Ca2+ channel blocker) but was unaffected by either omega-conotoxin GVIA (an N-type Ca2+ channel blocker) or -agatoxin IVA (a P/Q-type Ca2+ channel blocker). Combined blockade of N and P/Q channels with omega-conotoxin MVIIC did, however, block by 76% the protein expression. The inhibitory effects of fumidipine were partially reversed when the external Ca2+ concentration was raised from 1.6 to 5 mM. These findings, together with the fact that nicotinic receptor activation or Ca2+ release from internal stores also enhanced SNAP-25 protein expression, suggest that an increment of cytosolic Ca2+ concentration ([Ca2+]), rather than its source or Ca2+ entry pathway, is the critical signal to induce the protein expression. The greater coupling between L-type Ca2+ channels and protein expression might be due to two facts: (a) L channels contributed 50% to the global [Ca2+]i rise induced by 38 mM K+ in indo-1-loaded chromaffin cells and (b) L channels undergo less inactivation than N or P/Q channels on sustained stimulation of these cells.
García-Palomero
E
E
Instituto de Farmacología Teófilo Hernando, Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
Montiel
C
C
Herrero
C J
CJ
García
A G
AG
Alvarez
R M
RM
Arnalich
F M
FM
Renart
J
J
Lara
H
H
Cárdenas
A M
AM
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D004594:Electrophysiology; D005110:Extracellular Space / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D018722:Nicotinic Agonists / Q000494:pharmacology; D009994:Osmolar Concentration; D011188:Potassium / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D050825:Synaptosomal-Associated Protein 25; D020960:omega-Conotoxins / Q000494:pharmacology
D002121:Calcium Channel Blockers; D004095:Dihydropyridines; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018722:Nicotinic Agonists; D012333:RNA, Messenger; D050825:Synaptosomal-Associated Protein 25; D020960:omega-Conotoxins; D002110:Caffeine; D004246:Dimethylphenylpiperazinium Iodide; C082391:furnidipine; D011188:Potassium; D002118:Calcium