Norepinephrine increases Na-Ca exchange in rabbit abdominal aorta.
Na-Ca exchange was measured as intracellular Na+ (Na+i)-dependent 45Ca uptake in rabbit abdominal aortic rings. The amount of Na+i-dependent 45Ca uptake was proportional to both the concentration of Na+ in the Na(+)-loading solution and the concentration of Ca2+ in the assay medium. Na+i-dependent 45Ca uptake was inhibited by incorporation of Na+ in the assay medium and by amiloride analogues. Norepinephrine significantly enhanced the rate of 45Ca uptake in Na(+)-loaded tissue but had no effect on Na+i-independent 45Ca uptake. The effect of norepinephrine was prevented by phentolamine but not by propranolol. The stimulatory effect of norepinephrine was absent when the concentration of extracellular Ca2+(Ca2+o) was 0.3 mM or lower but became significant at 0.6 mM and higher. Na-Ca exchange was also increased by phorbol 12,13-dibutyrate but not by its inactive analogue (4 alpha-phorbol 12,13-didecanoate). 1-(5-Isoquinolinylsulfonyl)-2-methylpiperazine, an inhibitor of protein kinase C, blocked the stimulatory effect of norepinephrine on Na-Ca exchange. It is suggested that alpha-adrenoceptor stimulation increases Na-Ca exchange in rabbit abdominal aorta in a Na+i- and Ca2+o-dependent fashion. This effect is possibly mediated through the activation of protein kinase C.
Department of Pharmacology, University of Nevada School of Medicine, Reno 89557.
M A
MA
Khoyi
R A
RA
Bjur
D P
DP
Westfall
D000818:Animals; D001012:Aorta, Abdominal / Q000378:metabolism*; D002118:Calcium / Q000493:pharmacokinetics / Q000502:physiology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D066298:In Vitro Techniques; D008094:Lithium / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology; D019831:Sodium-Calcium Exchanger
D002352:Carrier Proteins; D019831:Sodium-Calcium Exchanger; D015240:Phorbol 12,13-Dibutyrate; D008094:Lithium; D012964:Sodium; D011493:Protein Kinase C; D002118:Calcium; D009638:Norepinephrine; D010646:Phentolamine