Pituitary adenylate cyclase-activating polypeptide increases [Ca2]i in rat gonadotrophs through an inositol trisphosphate-dependent mechanism.
Pituitary adenylate cyclase-activating polypeptide (PACAP) increases cAMP production and stimulates hormone release from a variety of anterior pituitary cells. However, in anterior pituitary gonadotrophs PACAP stimulates oscillations in cytosolic free Ca2+ concentration ([Ca2+]i) that appear to be independent of cAMP. To study the mechanisms involved in this response, we used the patch-clamp technique to microperfuse various agents into single rat gonadotrophs while monitoring [Ca2+]i with microfluorometry. Extracellular application of PACAP to single gonadotrophs stimulated high amplitude (> 1 microM) oscillations in [Ca2+]i, which were blocked by intracellular application of GDP beta S (guanosine 5'-O-2-thiodiphosphate), indicating the involvement of a G-protein. To identify the intracellular messenger(s) involved, we microperfused gonadotrophs with cAMP, inositol 1,4,5-trisphosphate (Ins(1,4,5)P3), or heparin, an antagonist of the Ins(1,4,5)P3 receptor. A high concentration of cAMP (100 microM) had no significant effect on basal [Ca2+]i and did not alter the PACAP-stimulated Ca2+ response. Heparin, but not its inactive isoform, completely blocked the PACAP-stimulated increase in [Ca2+]i, while Ins(1,4,5)P3 stimulated oscillations in [Ca2+]i very similar to those observed in response to PACAP. These results strongly suggest that PACAP mobilizes Ca2+ through an Ins(1,4,5)P3-dependent mechanism. The fact that PACAP stimulates two signaling pathways in pituitary cells could substantially enhance the signaling potential of this hypothalamic peptide.
Rawlings
S R
SR
Fondation pour Recherches Médicales, University of Geneva, Switzerland.
Demaurex
N
N
Schlegel
W
W
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D008297:Male; D009479:Neuropeptides / Q000037:antagonists & inhibitors / Q000502:physiology*; D018377:Neurotransmitter Agents / Q000037:antagonists & inhibitors / Q000502:physiology*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
C495403:Adcyap1 protein, rat; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D015544:Inositol 1,4,5-Trisphosphate; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D002118:Calcium