Activation of a beta-adrenergic-sensitive signal transduction pathway by the secosteroid hormone 1,25-(OH)2-vitamin D3 in chick heart.
In recent studies we have established that 1 alpha, 25-dihydroxy-vitamin D3[1,25(OH)2D3] rapidly stimulates dihydropyridine-sensitive calcium channel-mediated Ca2+influx in chick cardiac muscle by a non-genomic action which is accompanied by PKA-dependent phosphorylation of a 45 kDa microsomal membrane protein. To investigate the signal transduction pathway activated by 1,25(OH)2D3 in heart, we have compared the effects of the secosteroid hormone with those of the beta-adrenergic agonist isoproterenol (IPT) by employing cultured chick embryonic cardiac cells (myocytes) and thin-slice preparations of differentiated adult heart muscle. The increases in 45Ca2+ uptake and intracellular calcium ([Ca2+]i), cyclic AMP accumulation and changes in microsomal protein phosphorylation evoked by 1,25(OH)2D3 could be reproduced by IPT. When combined treatments with the sterol and the beta-adrenergic agonist were performed, no additive stimulation of these parameters was observed, suggesting that a common signal transduction pathway mediates the effects of 1,25(OH)2D3 and IPT. The participation of a guanine nucleotide binding protein (G protein) in the 1, 25(OH)2D3-induced changes in heart was investigated. AlF4(-), an activator of G proteins, and cholera and pertussis toxins, like 1, 25(OH)2D3 increased 45Ca2+ uptake by myocytes. AlF4(-) did not further stimulate the effects of 1,25(OH)2D3 thereby showing that a G protein is involved in the hormone action. Moreover, 1,25(OH)2D3 potentiated pertussis toxin but was unable to modify choleric toxin-dependent myocyte Ca2+ influx. Altogether, these results provide evidence indicating that the non-genomic action of 1,25(OH)2D3 on cardiac muscle calcium influx involves modulation of the beta-adrenergic-sensitive adenylyl cyclase/cAMP/PKA pathway coupled to a Gs protein.
Santillán
G E
GE
Bioquímica y Farmacia, Universidad Nacional del Sur, (8000) Bahía Blanca, Argentina.
Vazquez
G
G
Boland
R L
RL
D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002117:Calcitriol / Q000502:physiology*; D002478:Cells, Cultured; D002645:Chickens; D006321:Heart / Q000187:drug effects; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*
D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta; D002117:Calcitriol; D007545:Isoproterenol