Characterization of alpha 1-adrenoceptors which mediate chronotropy in neonatal rat cardiac myocytes.
1. In the present study, we investigated the effect of culture on alpha 1-adrenoceptors that mediate chronotropy and on alpha 1-adrenergic signal transduction in neonatal rat cardiac myocytes. 2. The spontaneous beating rate of neonatal rat myocytes after 3 or 7 days in culture was 37.4 +/- 4.2 or 102.0 +/- 4.3 beats min-1, respectively. The alpha 1-adrenoceptor-mediated chronotropic effect of norepinephrine was positive at day 3 of culture. In contrast to day 3 of culture, the neonatal myocytes exhibited a negative chronotropic response to norepinephrine on day 7 of culture. Both of these effects of norepinephrine were completely abolished by prazosin. 3. The affinity (Kd) and/or density (Bmax) of alpha 1-adrenoceptors labeled with [3H]prazosin in membranes from cultured myocytes were not significantly different between day 3 and day 7 of culture. 4. The expression of Gs, Gi, Gq and Go alpha-subunits in membranes from cultured myocytes was found to be significantly increased with the passage of culture time by immunoblot analysis. In contrast, no significant differences in G beta-subunit expression were observed between day 3 and day 7 of culture. 5. Norepinephrine-stimulated inositol 1,4,5-trisphosphate production by radio-binding protein in neonatal myocytes after 7 days of culture was significantly higher than that of the day 3 counterpart. 6. No significant changes in phospholipid and cholesterol contents in membranes from neonatal myocytes were observed with longer culture times.(ABSTRACT TRUNCATED AT 250 WORDS)
Kimura
H
H
Department of Pharmacology, Sapporo Medical University School of Medicine, Japan.
Miyamoto
A
A
Kawana
S
S
Ohshika
H
H
D000818:Animals; D000831:Animals, Newborn / Q000502:physiology*; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects*; D015151:Immunoblotting; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008566:Membranes / Q000378:metabolism; D009206:Myocardium / Q000166:cytology; D010743:Phospholipids / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D018340:Receptors, Adrenergic, alpha-1 / Q000187:drug effects / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects; D015016:Yohimbine / Q000378:metabolism
D010743:Phospholipids; D018340:Receptors, Adrenergic, alpha-1; D015016:Yohimbine; D015544:Inositol 1,4,5-Trisphosphate; D002784:Cholesterol; D019204:GTP-Binding Proteins; D011224:Prazosin