Leucine enkephalin antagonizes norepinephrine-induced 45Ca++ accumulation in rat atria.
Exposure of rat atrial slices to 10(-5) M norepinephrine (NE) for 10 minutes increases 45Ca++ accumulation from 1.64 +/- 0.10 to 2.23 +/- 0.06 nmol/mg tissue. In the presence of leucine enkephalin (10(-8) M), NE-stimulated 45Ca++ uptake is reduced to 1.44 +/- 0.10 nmol/mg tissue. The effect of leu-enkephalin is reversed in the presence of 10(-7) M naloxone, NE-stimulated 45Ca++ uptake being increased to 2.17 +/- 0.15 nmol/mg tissue. The results support a direct interaction of leu enkephalin with beta-agonist-stimulated Ca++ flux in rat atria, and correlate with the previously reported enkephalin antagonism of NE-induced positive chronotropy in the same tissue.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004743:Enkephalin, Leucine / Q000494:pharmacology*; D005260:Female; D006321:Heart / Q000187:drug effects; D006325:Heart Atria / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D009270:Naloxone / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors
D009270:Naloxone; D004743:Enkephalin, Leucine; D002118:Calcium; D009638:Norepinephrine