Pituitary adenylate cyclase-activating polypeptide induces a sustained increase in intracellular free Ca(2+) concentration and catechol amine release by activating Ca(2+) influx via receptor-stimulated Ca(2+) entry, independent of store-operated Ca(2+) channels, and voltage-dependent Ca(2+) channels in bovine adrenal medullary chromaffin cells.
Characteristics of pituitary adenylate cyclase-activating polypeptide (PACAP)-induced increase of Ca(2+) entry and catecholamine (CA) release were studied in bovine adrenal medullary chromaffin cells. PACAP induced intracellular free Ca(2+) concentration ([Ca(2+)](i)), showing an initial transient [Ca(2+)](i) rise followed by a sustained rise and CA release, which were not blocked by the blocking agents for nicotinic acetylcholine receptor (nAChR) channel, the voltage-dependent Ca(2+) channel (VOC), or the Na(+) channel. The sarcoendoplasmic Ca(2+)-ATPase inhibitors thapsigargin and cyclopiazonic acid did not affect the PACAP-induced sustained rise of [Ca(2+)](i), but did inhibit the initial [Ca(2+)](i) rise. In cells pretreated with cyclopiazonic acid or membrane-permeable, low-affinity Ca(2+) chelator N',N',N',N'-tetrakis(2-pyridylmethyl)ethylenediamine, PACAP further stimulated the entry of Ca(2+) or Mn(2+), whereas these treatments masked [Ca(2+)](i) dynamics induced by bradykinin. PACAP-induced sustained [Ca(2+)](i) rise and Mn(2+) entry were enhanced by acidic extracellular solution and reduced by alkalinization, whereas thapsigargin-induced Mn(2+) entry was regulated by the opposite. PACAP-induced [Ca(2+)](i) rise and Mn(2+) entry were not affected by blockers of cAMP-dependent protein kinase, phospholipase C, or protein kinase C. All store-operated Ca(2+) channel (SOC) blocking agents tested inhibited thapsigargin-induced Mn(2+) entry. 1(beta-[3-(4-Methoxyphenyl)-propoxy]-4-methoxyphenylethyl)-1H-imidazole hydrochloride (SK&F 96365), (R,S)-(3,4-dihydro-6,7-dimethoxy-isoquinoline-1-yl)-2-phenyl-N,N-di-[2-(2,3,4-trimethoxyphenyl)ethyl]-acetamide, and econazole inhibited PACAP-induced Ca(2+) or Mn(2+) entry, whereas GdCl(3), 7,8-benzoflavone, nor-dihydroguaiaretic acid, 5-nitro-2-(3-phenylpropylamino)benzoic acid, fulfenamic acid, and niflumic acid did not. SK&F 96365 and econazole but not GdCl(3) inhibited PACAP-induced CA release. These results suggest that PACAP activates a novel Ca(2+) entry pathway associated with sustained CA release independent of the nAChR channel, VOC and SOC, activated by acid pH, with different sensitivity to blockers of SOC. This pathway may provide a useful model for the study of receptor-operated Ca(2+) entry.
Morita
Katsuya
K
Department of Dental Pharmacology, Division of Integrated Medical Science, Graduate School of Biomedical Sciences, Hiroshima University, Kasumi 1-2-3, Minami-ku, Hiroshima 734-8553, Japan.
Sakakibara
Akira
A
Kitayama
Shigeo
S
Kumagai
Kei
K
Tanne
Kazuo
K
Dohi
Toshihiro
T
D000262:Adenylyl Cyclases / Q000378:metabolism; D000313:Adrenal Medulla / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D019439:Chromaffin Cells / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008345:Manganese / Q000378:metabolism; D009479:Neuropeptides / Q000494:pharmacology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011493:Protein Kinase C / Q000378:metabolism; D010738:Type C Phospholipases / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002395:Catecholamines; D007202:Indicators and Reagents; D009479:Neuropeptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D008345:Manganese; D011493:Protein Kinase C; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases; D002118:Calcium