title: Potentiating paired stimulation of cardiac muscle in vitro as positive inotropic reference standard.
abstract: In rabbit papillary muscles, potentiating paired stimulation was used as a standard positive inotropic intervention. Pairs of depolarizing electrical stimuli were applied, equal in strength and with a coupling interval of the functional refractory period plus 10 msec. After five successive pairs at a basic driving rate of 0.5 Hz, maximum potentiation amounting to a two- to threefold increase in the contraction amplitude was reached. The potentiating paired stimulation was rapid in both onset and reversibility and was reproducible. Potentiating paired stimulation is sparing since internal Ca2+ pools are utilized to increase force. Using potentiating paired stimulation-induced increase in force of contraction as a new reference, the following order of potency of positive inotropic agents was obtained: ouabain greater than DPI 201-106 greater than IBMX greater than APP 201-533. Effects of these drugs on rested-state contractions and frequency-force relationship were also investigated.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology; D004558:Electric Stimulation; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D011728:Pyridones / Q000494:pharmacology; D011817:Rabbits; D016276:Ventricular Function
chemical_list: D002316:Cardiotonic Agents; D010879:Piperazines; D011728:Pyridones; D010042:Ouabain; C045982:3-amino-6-methyl-5-phenyl-2(1H)-pyridinone; C046261:DPI 201-106; D015056:1-Methyl-3-isobutylxanthine