title: Beta-adrenergic receptor characteristics of postnatal rat myocardial cell preparations.
abstract: Primary myocardial cell cultures and freshly isolated cardiac cells in suspension represent two isolated, whole cell models for investigating cellular transsarcolemmal 45Ca++ exchange in response to a receptor-coupled stimulus. Studies were performed to characterize beta-adrenergic receptor binding, beta-adrenergic receptor mediated cellular calcium (45Ca++) exchange, and viability in purified primary myocardial cell cultures and freshly isolated cardiac cells in suspension obtained from 3- to 5-d-old Sprague-Dawley rats. In addition, beta-adrenergic receptor binding was characterized in whole-heart crude membrane preparations. All three preparations had saturable beta-adrenergic binding sites with the antagonist [125I]iodopindolol [( 125I]IPIN). The suspensions had a significantly lower Bmax (42 +/- 6 fmol/mg protein) than the membranes and cultures (77 +/- 8 and 95 +/- 10 fmol/mg protein, respectively). The KD of the cultures (218 +/- 2.0 pM) was significantly higher than that for the suspensions (107 +/- 1.3 pM) and membranes (93 +/- 1.3 pM). Viability was significantly lower in the suspensions (57%) when compared to 94% viability in myocardial cell cultures after 3 h of incubation in Kreb's Henseleit buffer. Incubation of the cultures with 5.0 X 10(-7) M isoproterenol resulted in a significant increase in 45Ca++ exchange as early as 15 s. In contrast, 45Ca++ exchange into the suspensions was not increased. Although both primary cell cultures and cardiac cells in suspension possess saturable beta-adrenergic receptors, only the monolayer cultures exhibited functional beta-adrenergic receptor-mediated 45Ca++ exchange. Of the two intact cell models investigated, these data suggest that primary myocardial cell cultures are more suitable than cell suspensions for investigating beta-adrenergic receptor binding and functions in the postnatal rat heart.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Texas, Austin 78712.
authors.forename: A A
authors.initials: AA
authors.lastname: Welder
authors.forename: T
authors.initials: T
authors.lastname: Machu
authors.forename: S W
authors.initials: SW
authors.lastname: Leslie
authors.forename: R E
authors.initials: RE
authors.lastname: Wilcox
authors.forename: J
authors.initials: J
authors.lastname: Bradlaw
authors.forename: D
authors.initials: D
authors.lastname: Acosta
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D002470:Cell Survival; D002474:Cell-Free System; D002478:Cells, Cultured; D006321:Heart / Q000502:physiology*; D007700:Kinetics; D009200:Myocardial Contraction; D009206:Myocardium / Q000166:cytology*; D051381:Rats; D011943:Receptors, Adrenergic, beta / Q000502:physiology*
chemical_list: D011943:Receptors, Adrenergic, beta; D002118:Calcium