| 11003581 |
Emala CW, Clancy-Keen J, Hirshman CA: Decreased adenylyl cyclase protein and function in airway smooth muscle by chronic carbachol pretreatment. Am J Physiol Cell Physiol. 2000 Oct;279(4):C1008-15.
Cellular levels of cAMP are an important determinant of airway smooth muscle tone. We have previously shown that chronic (18 h) but not acute (30 min or 2 h) pretreatment with the muscarinic receptor agonist carbachol resulted in decreased adenylyl cyclase activity in response to GTP, isoproterenol, or forskolin via a pathway blocked by the protein kinase C inhibitor staurosporine. The present study was designed to determine if carbachol-induced decreases in adenylyl cyclase activity were due to regulatory events at the level of either G (s) alpha or adenylyl cyclase. Detergent-solubilized G (s) alpha from control or carbachol-pretreated bovine airway smooth muscle had similar adenylyl cyclase activity in response to either NaF or guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) when reconstituted into S49 cyc (-) membranes that lack endogenous G (s) alpha (carbachol pretreated: GTPgammaS, 93 +/- 13% of control; NaF/AlCl (3), 99 +/- 8.6% of control; n = 4). Exogenous G (s) alpha solubilized from red blood cells failed to restore normal adenylyl cyclase activity when reconstituted into carbachol-pretreated bovine airway smooth muscle (carbachol pretreated: GTP, 36 +/- 10% of control; NaF/AlCl (3), 54 +/- 11% of control; n = 4). [(3) H] forskolin radioligand saturation binding assays revealed a decreased quantity of total adenylyl cyclase protein after carbachol pretreatment (maximal binding: 152 +/- 40 and 107 +/- 31 fmol/mg protein in control and carbachol-pretreated airway smooth muscle, respectively). These results suggest that chronic activation of muscarinic receptors downregulates the expression of adenylyl cyclase protein in bovine airway smooth muscle. |
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