Intracellular calcium involvement in pituitary adenylate cyclase-activating polypeptide stimulation of growth hormone and gonadotrophin secretion in goldfish pituitary cells.
The involvement of intracellular Ca(2+) stores and their regulatory mechanisms in mediating pituitary adenylate cyclase-activating polypeptide (PACAP) stimulation of growth hormone (GH) and maturational gonadotrophin (GTH-II) secretion from goldfish pituitary cells was investigated using a cell column perifusion system. Pretreatment with caffeine abolished the GH and GTH-II responses to PACAP. Dantrolene attenuated PACAP-elicited GTH-II release but did not affect the GH response, whereas ryanodine and 8-bromo-cADP ribose did not alter PACAP-induced GH and GTH-II release. Two endoplasmic/sarcoplasmic reticulum Ca(2+) ATPase (SERCA) inhibitors, thapsigargin and cyclopiazonic acid, augmented PACAP-induced GTH-II release; similarly, thapsigargin elevated GH responses to PACAP. Treatment with carbonyl cyanide m-chlorophenylhydrazone, a mitochondrial uncoupler, reduced PACAP-stimulated GH release; however, inhibition of the mitochondrial Ca(2+) uniport by Ru360 did not affect GH and GTH-II responses. The phosphatidyl inositol (PI)-specific phospholipase C (PLC) inhibitor ET-18-OCH(3) inhibited, whereas the phosphatidyl-choline (PC)-specific PLC inhibitor D609 enhanced, PACAP-stimulated GH and GTH-II responses. On the other hand, the IP(3) receptor blocker xestospongin D had no effect on PACAP-induced GTH-II response and potentiated the GH response. These results suggest that, despite some differences between GH and GTH-II cells, PACAP actions in both cell types generally rely on a caffeine-sensitive, but a largely ryanodine receptor-independent, mechanism. PC-PLC and some SERCA negatively modulate PACAP actions but mitochondrial Ca(2+) stores per se are not important. A novel PI-PLC mechanism, which does not involve the traditional IP(3)/Ca(2+) pathway, is also suggested.
Sawisky
G R
GR
Department of Biological Sciences, University of Alberta, Edmonton, Canada.
Chang
J P
JP
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D036563:Cyclic ADP-Ribose / Q000031:analogs & derivatives* / Q000494:pharmacology; D003620:Dantrolene / Q000494:pharmacology; D005260:Female; D006054:Goldfish; D006065:Gonadotropins, Pituitary / Q000378:metabolism*; D013006:Growth Hormone / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009125:Muscle Relaxants, Central / Q000494:pharmacology; D009479:Neuropeptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors; D012433:Ryanodine / Q000494:pharmacology; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors
C493642:8-bromo-cyclic-ADP-ribose; D015220:Calcium Channels; D006065:Gonadotropins, Pituitary; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009125:Muscle Relaxants, Central; D009479:Neuropeptides; D010446:Peptide Fragments; D010726:Phosphodiesterase Inhibitors; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D018160:Receptors, Cytoplasmic and Nuclear; C108046:pituitary adenylate cyclase-activating-peptide (1-38), pig; D036563:Cyclic ADP-Ribose; D012433:Ryanodine; D002110:Caffeine; D013006:Growth Hormone; D010738:Type C Phospholipases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D003620:Dantrolene; D002118:Calcium