Neurogenic and myogenic contractile responses of dog mesenteric arteries to reduced K+ concentration and their interactions with ouabain.
Maintained reduction in extracellular K+ concentrations [( K]e) of isolated canine mesenteric arteries produced two contractions separated by a period of several hours. The mechanisms for respective early and late contractions were investigated. First, early responses to reduced [K]e were examined quantitatively over a period of 2 hr. Critical [K]e for initiating the contraction was 0.14 mM. Early contractions induced by K-free solution were abolished by phentolamine (10(-6) M) or reserpine pretreatment (0.5 mg/kg) but were not inhibited by cocaine (3 X 10(-6) M) or bretylium (2 X 10(-5) M). Treatment with ouabain at a low concentration of 2 X 10(-7) M potentiated markedly the phentolamine-sensitive contractile response to reduced [K]e. In contrast, contractile responses to norepinephrine, tyramine and transmural electrical stimulation were not potentiated by ouabain. Second, the late contraction, that occurred 4 to 5 hr after K-free substitution, also occurred in arteries pretreated with phentolamine or reserpine. The phentolamine-resistant late contraction was not inhibited by atropine, chlorpheniramine, cimetidine, saralasin, aspirin or methysergide. Ouabain potentiated the late contractile response to reduced [K]e in the presence of phentolamine. Thus, in canine mesenteric arteries, reduction in [K]e causes an early contraction due to norepinephrine release from adrenergic nerves and a late contraction that appears to be of myogenic origin. Ouabain may enhance both neurogenic and myogenic derived contractions in response to reduced [K]e by exaggerating the inhibition of the Na+,K+ exchange pump in the membranes of adrenergic nerves and vascular smooth muscle.
D000818:Animals; D001950:Bretylium Tosylate / Q000494:pharmacology; D003042:Cocaine / Q000494:pharmacology; D004285:Dogs; D005260:Female; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D009638:Norepinephrine / Q000378:metabolism; D010042:Ouabain / Q000494:pharmacology*; D010646:Phentolamine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D012110:Reserpine / Q000494:pharmacology; D013997:Time Factors
D010042:Ouabain; D001950:Bretylium Tosylate; D012110:Reserpine; D003042:Cocaine; D011188:Potassium; D009638:Norepinephrine; D010646:Phentolamine