Inotropic mechanisms in mammalian myocardium. With special reference toeffects produced by acid base changes and altered stimulation frequency.
Journal/Book: THESIS,-LUND, 1974, (32p.).. 1974;
Abstract: It was the aim of the investigation to gain further insight into some ofthe mechanisms by which cardiac muscle alters its inotropic state. Theresults are summarized. Viscotoxins A3 and B, in low concentrations(10sup -sup 7 to 10sup -sup 6 mol/l), reduced the isometric twitch andproduced contracture and progressive depolarization of rabbit papillarymuscle. These changes were almost completely reversed by increasing theextracellular calcium concentration from 2.0 to 4.0 nmol/l. Whenextracellular pH was lowered from 7.4 to 7.0 and 6.7 in a bathingsolution buffered with histidine (10 mmol/l), the active force decreasedat all contraction frequencies studied (12, 60 and 120/min). A loweringof the extracellular pH from 7.4 to 6.7 did not alter the restingmembrane potential or action potential characteristics. After anincrease of HCOsub 3sup - concentration and PCOsub 2 at constantextracellular pH the active force of the muscle increased at low anddecreased at high contraction frequencies. This acid base change alsocaused a marked abbreviation of the action potential. The bicarbonateion was found to be responsible for the abbreviation of the actionpotential and the positive inotropic effect at low concentrationfrequencies. The force frequency curve at steady state for rabbitpapillary muscle exhibited a maximum at approximately 4 stimuli/sec. Thetwitch amplitude in response to a test stimulus applied at differenttimes (test pulse interval) after a stimulation period was also studied.A two compartment model of the cellular calcium metabolism is used toexplain the force frequency relationship in mammalian myocardium.COPYRIGHT BY Elsevier Science BV, Amsterdam, Netherlands END OF DOCUMENT