Isoproterenol brings about a rapid transient relaxation of depolarized ileal smooth muscle as well as a longer lasting decline in tension. Only the latter effect is mimicked by dibutyryl cyclic AMP or by phosphodiesterase inhibitors. Beta adrenergic blocking agents cause a rapid transient contraction in preparations relaxed by isoproterenol but not in preparations relaxed by the other agents, and this effect persists when influx of Ca2+ from the extracellular space is prevented. The transient component of the isoproterenol-induced relaxation is therefore attributed to sequestration of Ca2+ at intracellular sites, and the contraction which follows the subsequent addition of beta blocking agents is due to release of Ca2+ from these sites.
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)
- Pharmacology, Toxicology and Pharmaceutics(all)