Calmodulin-dependent adenylate cyclase activity in rat cerebral cortex: effects of divalent cations, forskolin and isoprenaline.
The role of calcium-calmodulin (Ca2+-CaM) in the modulation of beta-adrenergic adenylate cyclase activity in rat cerebral cortex has been studied. In addition, the effects of manganese (Mn2+) and forskolin on CaM-dependent enzyme activity were investigated. At 2 mM magnesium (Mg2+) low concentrations of Ca2+ stimulated the enzyme activity (Ka 0.25 +/- 0.08 microM), whereas higher Ca2+ levels (greater than 2 microM) inhibited the activity. No activating effect of Ca2+ was observed in CaM-depleted membranes, but the inhibitory effect persisted and the stimulatory action of Ca2+ could be restored by addition of exogenous CaM. The ability of Ca2+ to activate the enzyme was reduced by increasing concentrations of Mg2+. At 10 mM Mg2+ the apparent Ka of Ca2+ was 0.55 +/- 0.16 microM and half-maximal inhibition was observed at 80-120 microM Ca2+. A synergistic effect was observed between Ca2+ and isoprenaline on the adenylate cyclase activity. Calcium did not alter the apparent Ka of isoprenaline (0.9 +/- 0.27 microM) and isoprenaline did not change the apparent Ka of Ca2+. However, isoprenaline decreased the apparent Ka of CaM; 0.11 +/- 0.07 micrograms vs. 0.32 +/- 0.1 micrograms (0.5 ml assay mixture)-1, with and without isoprenaline, respectively. A synergistic effect was also observed between Ca2+ and forskolin, but no change in their apparent Ka values was found. Furthermore, Mn2+ was found to activate the enzyme through CaM. These data demonstrate that Ca2+ -CaM potentiates beta-adrenergic adenylate cyclase activity and thus is able to modulate neurotransmitter stimulation in cortex. Furthermore, both forskolin and Mn2+ affect CaM-dependent enzyme activity. Forskolin potentiates Ca2+-CaM stimulation, while Mn2+ increases the activity by activating the enzyme through CaM.
Mørk
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Department of Pharmacology, University of Copenhagen, Denmark.
Geisler
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D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002147:Calmodulin / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects / Q000201:enzymology*; D005576:Colforsin / Q000494:pharmacology*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D008345:Manganese / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism
D002147:Calmodulin; D002413:Cations, Divalent; D011943:Receptors, Adrenergic, beta; D005576:Colforsin; D008345:Manganese; D000262:Adenylyl Cyclases; D008274:Magnesium; D007545:Isoproterenol; D002118:Calcium