title: Effects of beta-adrenergic stimulation on calcium movements in rabbit aortic smooth muscle: relationship with cyclic AMP.
abstract: 1. The effects of isoprenaline (10(-6) M) on relaxation, unidirectional as well as net Ca(2+) fluxes, and cyclic AMP levels were investigated in rabbit aorta under the condition of high-K(+) depolarization in the presence of phentolamine (10(-5) M).2. Isoprenaline (10(-6) M) caused significant inhibition of Ca(2+) influx stimulated by 145 mM-K(+) (0 Na(+)) solution. The time courses of Ca(2+) influx inhibition and relaxation by isoprenaline were parallel. Isoprenaline also caused a significant inhibition of high-K(+)-induced gain in net Ca(2+) content.3. Ro 20-1724 (1 mM), a phosphodiesterase inhibitor, also caused relaxation and Ca(2+) influx inhibition in high-K(+)-depolarized rabbit aorta. Pre-treatment with Ro 20-1724 potentiated isoprenaline-induced Ca(2+) influx inhibition and relaxation.4. Isoprenaline and Ro 20-1724 each alone increased cyclic AMP levels. Furthermore pre-treatment with Ro 20-1724 caused potentiation of isoprenaline-induced increases in cyclic AMP levels.5. At submaximal concentration, D600 (10(-7) M) caused partial inhibition of high-K(+)-stimulated Ca(2+) influx and produced relaxation. However, unlike Ro 20-1724, it did not potentiate isoprenaline-induced Ca(2+) influx inhibition and relaxation. D600 does not increase cyclic AMP levels in smooth muscle.6. Dibutyryl cyclic AMP (1 mM), a lipid-soluble analogue of cyclic AMP, caused relaxation and inhibited high-K(+)-stimulated Ca(2+) influx.7. Isoprenaline failed to cause stimulation of Ca(2+) efflux in high-K(+)-depolarized rabbit aorta.8. It is concluded that the inhibition of Ca(2+) influx may be one of the mechanisms by which beta-receptor stimulation can reduce intracellular free Ca(2+) to promote relaxation of smooth muscle. The data support the involvement of cyclic AMP in this action of the beta-agonist.9. Since the experiments were conducted in 145 mM-K(+) (0 Na(+)) depolarizing conditions, the role of hyperpolarization or of a Na(+)-Ca(2+) exchange mechanism in isoprenaline-induced Ca(2+) influx inhibition and/or relaxation can be excluded.
mesh_terms: D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000818:Animals; D001011:Aorta / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D011817:Rabbits
chemical_list: D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D003994:Bucladesine; D000242:Cyclic AMP; D007545:Isoproterenol; D011188:Potassium; D002118:Calcium