Dual regulation of human syncytial adenylyl cyclase.
The dual (stimulatory and inhibitory) regulation of adenylyl cyclase was studied in syncytiotrophoblast basal membranes prepared from term human placenta. Stimulation of adenylyl cyclase activity with GTP, non-hydrolyzable GTP analogs, isoproterenol and PGE1 was observed, confirming the presence of an intact stimulatory pathway in these membranes. Investigations of the inhibitory pathway revealed tight coupling of the G-protein, Gi alpha, to catalytic adenylyl cyclase, with high doses of GTP producing 80 per cent inhibition of GTP/forskolin-stimulated activity. Confirming Gi alpha involvement, pertussis toxin (PTX) treatment of basal membranes augmented the responses of adenylyl cyclase to both GTP and forskolin. In addition, immunoblotting of basal membrane proteins revealed the presence of the G-protein subunits, Gs alpha, Gi alpha, and G beta/gamma. The response of adenylyl cyclase was measured to a series of agonists known to inhibit adenylyl cyclase in other tissues, however a reproducible inhibitory effect was produced only by somatostatin (approximately 80 per cent). Treatment of basal membranes with PTX caused a degree of reversal of the somatostatin-mediated adenylyl cyclase inhibition. However, the intoxication was insufficient to restore GTP/forskolin-stimulated activity.
Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, San Francisco 94143-0550.
M M
MM
Jacobs
X
X
Li
N P
NP
Illsley
D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism*; D016477:Artifacts; D004591:Electrophoresis, Polyacrylamide Gel; D005260:Female; D019204:GTP-Binding Proteins / Q000032:analysis; D015726:Giant Cells / Q000201:enzymology*; D006150:Guanine Nucleotides / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D037342:Pertussis Toxin; D010920:Placenta / Q000201:enzymology*; D011247:Pregnancy; D013004:Somatostatin / Q000037:antagonists & inhibitors; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D037361:Adenylate Cyclase Toxin; D006150:Guanine Nucleotides; D010566:Virulence Factors, Bordetella; D013004:Somatostatin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases