Calcium fraction correlating with contractile force of ventricular muscle of guinea-pig heart

Abstract

Ca shifts in the isolated, perfused ventricular muscle of guinea-pig hearts were investigated with the aid of 45Ca under the conditions of complete equilibration of preparations with the isotope-containing solution. In some series of experiments total Ca content was also measured by means of atomic absorption spectrophotometry. The content of 45Ca at the end of 70 min equilibration period during which the ventricles were stimulated at a rate of 60/min was 1.66 +/- 0.09 mmol/kg w.w. This content dropped to 0.42 +/- 0.09 mmol/kg w.w. within 4 min of rest. Contractile force also decreased to 21% of control. Both the content of 45Ca and contractile force returned to the pre-rest values within the 4 min of post-rest stimulation. The difference between the total Ca content in the rested and stimulated muscle was comparable to the respective difference in 45Ca contents. A significant linear correlation between this 45Ca fraction which was lost at rest and recovered during the post-rest stimulation, and contractile force was found under the following experimental conditions: I. post-rest recovery, II. decay during rest, III. post-rest stimulation at various rates. These results are consistent with the hypothesis proposing that this Ca fraction is involved in the frequency-dependent control of contractile force.

Rest- and stimulation-dependent changes in exchangeable calcium content in rabbit ventricular myocardium

“…Hence we proposed that Ca 2 fraction might be intimately involved in the mechanism of slow, force-frequency relations as already postulated by Chapman and Niedergerke for the frog heart (5). Results of the comparative experiments performed previously on the guinea pig (17,12) and rat (11) ventricular *) This study was supported by the grant CPBR, 11.6 myocardium and on guinea pig atrial muscle (16) have shown that the response of the volume of Ca2 fraction to the prolonged rest and post-rest stimulation parallel the respective responses of CF whose pattern varies from species to species, and from one part of the heart to another.…”

“…Experiments were performed on isolated, vascularly perfused ventricles of hearts from New Zealand white rabbits (1.4-1.9 kg), according to the methods described in detail elsewhere (17,12). Briefly, the hearts were isolated and perfused by Langendorff method with Tyrode solution of the following composition (in mM): NaCI, 137; KCI, 7.40; CaCI2, 1.80; MgCI,, 1.05; NaH2PO4, 0.43; NaHCOs, 11.90; glucose 11.00. pH of the solution when gassed with 5% CO2 in 95% 02 was 7.35.…”

“…The first post-rest contraction (RSC) resulted in a gain of 0.073 mmo145Ca/kg w.w. Both the content of ~SCa and CF returned to the pre-rest values when stimulation was resumed.The difference between the aSCa content of post-rest stimulated and rested preparations (0.384 mmol/ kg w.w.) is equivalent to Ca2 fraction (Ca2), previously described in guinea pig ventricular myocardium (17,12). However, the volume of rabbit Ca z is only about 42 % of that in guinea pig.…”

Net transsarcolemmal Ca2+ shifts versus Ca/Ca exchange in guinea pig ventricular muscle

“…The hearts were perfused with the 45Ca-containing solution for the next 60 min and stimulated at the rate of 60/min, which assured complete equilibration of the tissue Ca 2t exchangeable with 45Ca (19). Thereafter, in all experiments, stimulation was stopped and the heart was perfnscd with one of the solutions listed below: A) Tyrode solution containing 4SCa and 0.1 mM vanadate; B) Tyrode solution containing 0.1 mM vanadate (no 4SCa); C) No Na t solution containing (in mM): CaCI2 1.8; MgCI 2 1.05; KCI 7.8; glucose i1; Tris-HC1 10; sucrose 243; vanadate 0.1 and 45Ca; D) C (no Na t) solution without 45Ca; E) Low Ca 2+ solution containing (in mM): free Ca 2+ 0.01; free Mg 2+ 1; free K + 7.5; free Na § 140; TRIS-HCI 10; EGTA 0.1; glucose 11; vanadate 0.1, and 45Ca; F) Low Ca 2t solution (E) without 45Ca; G) Low Ca 2t, no Na + solution: the E solution in which 1 mM NaCI was substituted by 1.84 mM sucrose (22); and H) Low Ca 2+, no Na + solution: the G solution without 45Ca.…”

“…The transsarcolemmal Ca 2+ fluxes remain a subject of wide interest (3,13,16,18,19,23,25). One approach to the investigation of these Ca 2 § fluxes is by use of the isotope 45Ca.…”