Modulations of early and late secretory processes by activation of protein kinases in the rat adrenal medulla.
Modulatory effects of the activation of either protein kinase C (PKC) by phorbol 12,13-dibutyrate (PDBu) or protein kinase A (PKA) by forskolin on stimulant-evoked secretory processes in the perfused rat adrenal medulla were studied. PDBu or forskolin was applied during repetitive stimulation (30 s each at 10-min intervals) with nicotine, bradykinin, muscarine or histamine, and changes in [Ca2+]i (fura-2 microfluorometry) and catecholamine secretions (electrochemical detection) were simultaneously measured. PDBu markedly potentiated the nicotine-evoked secretion without altering the [Ca2+]i response. PDBu partially inhibited the muscarine-evoked secretion and almost completely blocked the histamine-evoked secretion, concomitantly with extensive suppressions of the [Ca2+]i responses to these stimulants. The bradykinin-evoked secretion was enhanced by PDBu despite a slight attenuation of the [Ca2+]i response. PDBu reduced bradykinin-induced intracellular Ca2+ release in a Ca2+-free medium but enhanced the secretion associated with the released Ca2+. These results suggest that PDBu-activated PKC modulates secretory processes at, at least, two different stages. An early-stage modulation may downregulate receptor/G protein systems, which accounts for the inhibitory effect of PDBu on the muscarine- and histamine-evoked responses. A late-stage modulation may generally promote Ca2+-triggered exocytosis after elevation of [Ca2+]i, which explains the potentiation of the nicotine-evoked secretion by PDBu. The late-stage modulation may counteract the early-stage modulation in bradykinin-stimulated cells. Forskolin potentiated the secretory responses to the four secretagogues without increasing the [Ca2+]i responses. PKA may modulate secretory process at a step(s) distal to the rise in [Ca2+]i as is the case with the late-stage modulation by PKC.
Warashina
A
A
Department of Physiology, Niigata University School of Medicine, Asahimachi-dori, Niigata, Japan.awarashi@med.niigata-u.ac.jp
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000313:Adrenal Medulla / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism*; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D009116:Muscarine / Q000494:pharmacology; D009538:Nicotine / Q000494:pharmacology; D010477:Perfusion; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002395:Catecholamines; D005576:Colforsin; D015240:Phorbol 12,13-Dibutyrate; D009538:Nicotine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009116:Muscarine; D006632:Histamine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D001920:Bradykinin; D002118:Calcium