Concanavalin A amplifies both beta-adrenergic and muscarinic cholinergic receptor-adenylate cyclase-linked pathways in cardiac myocytes.
Concanavalin A (Con A) is a tetrameric plant lectin that disrupts plasma membrane-cytoskeletal interactions and alters plasma membrane fluidity. We used Con A as a probe to explore beta-adrenergic and muscarinic cholinergic receptor-mediated regulation of cAMP in intact neonatal rat ventricular myocytes. Preincubation with Con A, 0.5 micrograms/ml, attenuated 1 microM (-)-norepinephrine (NE)-induced downregulation of beta-adrenergic receptors and resulted in a 50% augmentation of cAMP accumulation stimulated by 1 microM NE. Con A also augmented forskolin (1-10 microM)-stimulated cAMP accumulation by an average of 37% (P less than 0.05); however, Con A preincubation had no effect on basal or cholera toxin-stimulated cAMP content. The muscarinic cholinergic agonist carbachol (1-100 microM) decreased 1 microM NE-stimulated cAMP generation by an average of 32% (n = 7, P less than 0.05); preincubation with Con A further enhanced the inhibitory effect of carbachol by 18% (n = 7, P less than 0.05). Carbachol (1 microM) for 2 h decreased muscarinic cholinergic receptor density in whole cells by 33%; preincubation with Con A prevented this receptor downregulation. Con A pretreatment did not affect (-)-isoproterenol- or forskolin-stimulated adenylate cyclase activity in cell homogenates, suggesting that an intact cytoarchitecture is necessary for Con A to augment cAMP formation. We conclude that Con A, through its modulation of beta-adrenergic and muscarinic cholinergic receptor signaling, amplifies both stimulatory and inhibitory adenylate cyclase-linked pathways in intact neonatal ventricular myocytes. These data suggest the possibility that plasma membrane-cytoskeletal interaction is an important regulator of transmembrane signaling because interference with this interaction results in alterations in cAMP accumulation mediated by both beta-adrenergic- and muscarinic cholinergic-adenylate cyclase pathways.
Rocha-Singh
K J
KJ
Cardiology Section, Department of Veterans Affairs Medical Center, San Francisco, CA 94121.
Hines
D K
DK
Honbo
N Y
NY
Karliner
J S
JS
D000262:Adenylyl Cyclases / Q000032:analysis*; D000818:Animals; D002478:Cells, Cultured; D003208:Concanavalin A / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D019204:GTP-Binding Proteins / Q000502:physiology; D006321:Heart / Q000187:drug effects*; D008358:Mannose / Q000494:pharmacology; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000032:analysis / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000032:analysis / Q000187:drug effects*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D011943:Receptors, Adrenergic, beta; D011976:Receptors, Muscarinic; D003208:Concanavalin A; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D013755:Tetradecanoylphorbol Acetate; D008358:Mannose