Glucagon-induced changes in the action potential, contraction, and Na+-K+-ATPase of cardiac muscle.
The effects of glucagon in concentrations of 0.294 times 10(-6) mol/l, 1.47 times 10(-6) mol/l; 2.94 times 10(-6) mol/l, 5.8 times 10(-6) mol/l, and 1.47 times 10(-5) mol/l on the simultaneously recorded action potentials and contractions; and microsomal and sarcolemmal Na+-tk+-atpase in the myocardium of the guinea pig, rabbit, dog, and pig were investigated. Glucagon in all the concentrations produced an inhibition of the Na+-K+-ATPase associated with an increase in the contractility and shortening of the duration of action potential in dog myocardium. The increase in contraction was concentration-dependent up to a certain concentration. Inhibition of sarcolemmal ATPase was more than that of microsomal ATPase. In none of the concentrations did glucagon produce any significant changes in the Na+-K+-ATPase. In none of the concentrations did glucagon produce any significant changes in the Na+-K+-ATPase, contractility, and action potential duration in the myocardium of guinea pig, rabbit, or pig. These results suggest that glucagon-induced positive inotropic effect might be due to an increase in the Ca++ influx as a result of inhibition of membrane Na+-K+-ATPase. Shortening of the action potential duration might also be due to an increased efflux of potassium as a result of an inhibition of Na+-K+-ATPase.
D000200:Action Potentials / Q000187:drug effects*; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D002118:Calcium; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005934:Glucagon / Q000494:pharmacology*; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D008861:Microsomes / Q000201:enzymology; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000201:enzymology*; D010210:Papillary Muscles / Q000187:drug effects; D011188:Potassium; D011817:Rabbits; D012508:Sarcolemma / Q000201:enzymology; D012964:Sodium; D013552:Swine
D005934:Glucagon; D012964:Sodium; D000251:Adenosine Triphosphatases; D011188:Potassium; D002118:Calcium