title: Sodium requirement for the positive inotropic action of isoproterenol on guinea pig atria.
abstract: Isoproterenol doses not elicit its characteristic positive inotropic action in contracting guinea pig atria suspended in sodium-free media. However, the ability of isoproterenol to decrease the time to peak tension development during an individual contraction cycle is still present in sodium-free solutions. Removal of sodium diminished but did not eliminate the tissues' ability to elevate adenosine 3',5'-monophosphate in response to isoproterenol. The striking absence of an inotropic action by isoproterenol on atria in sodium-free media suggests that sodium (and possibly a sodium-calcium exchange across the sarcolemma) plays an important role in the inotropic action of catecholamines.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D012508:Sarcolemma / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology*
chemical_list: D010726:Phosphodiesterase Inhibitors; D012964:Sodium; D000242:Cyclic AMP; D007545:Isoproterenol; D002118:Calcium