title: Involvement of calmodulin in the regulation of adenylate cyclase activity in guinea-pig enterocytes.
abstract: The involvement of calmodulin as an activator of adenylate cyclase activity was examined in isolated guinea-pig enterocytes and in a membrane preparation. In enterocytes, which responded to prostaglandin E1, vasoactive intestinal peptide and cholera toxin with a significant increase in the rate of cAMP formation trifluoperazine, a calmodulin antagonist, completely inhibited cAMP formation. In a membrane preparation adenylate cyclase activity was stimulated 10-20-fold by the GTP analog, guanosine 5'-[beta-imido]5'-triphosphate (Gpp[NH]p). Prostaglandin E1 and vasoactive intestinal peptide enhanced cAMP formation in this system by 2-3- and 1.2-1.6-fold. respectively. Addition of 200 nM calmodulin to membranes, in which endogenous calmodulin was decreased from 1.4 microgram/mg protein to 0.5 microgram/mg protein by washing with buffer containing EGTA and EDTA, resulted in a 3-4-fold increase of adenylate cyclase activity. The absolute increment in adenylate cyclase activity caused by calmodulin (10-15 pmol cAMP/min per mg protein) was approximately the same in the absence or presence of Gpp[NH]p. The apparent Ka for Gpp[NH]p (6 . 10-7 M) was not significantly changed by the addition of calmodulin. Although endogenous calcium (approx. 10 microM) in the enzyme assay was adequate to affect stimulation by calmodulin, a maximal effect was observed at a calcium concentration of 100 microM. These findings indicate that a calmodulin-sensitive form of adenylate cyclase is present in guinea-pig enterocytes, and that stimulation of cAMP formation in the intestinal mucosa may involve a calmodulin-mediated mechanism.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000527:Alprostadil; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism* / Q000494:pharmacology; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D007421:Intestine, Small / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D007700:Kinetics; D008297:Male; D011458:Prostaglandins E / Q000494:pharmacology; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology
chemical_list: D002135:Calcium-Binding Proteins; D002147:Calmodulin; D011458:Prostaglandins E; D006165:Guanylyl Imidodiphosphate; D014660:Vasoactive Intestinal Peptide; D002772:Cholera Toxin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D000527:Alprostadil; D002118:Calcium; D015056:1-Methyl-3-isobutylxanthine