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KMID : 0377519810060020217
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Chung-Ang Journal of Medicine
1981 Volume.6 No. 2 p.217 ~ p.224
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Effect of Low Sodium Solution on Intracelluar Calcium Pool of Cardiac Muscle
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Lee Young-Bae
Cho Sung-Il
Rhee Sang-Don
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Abstract
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In order to investigate the effect of low sodium (79 mM) Tyrode solution on intracellular calcium pool of cardiac muscle, a rabbit ventricular papillary muscle preparation was excised out to a in vitro contraction chamber and the isometric contraction of the preparation was recorded in a normal Tyrode solution by a control stimuli (1 Hz.)and then the intracellular calcium was activated by a priming (5 Hz.) stimuli for 5 seconds. After the priming stimuli, rest period for I to 320 seconds were applied and the amplitude of a contraction by a test stimulus over that by a previous control stimuli were plotted in a semi-logarithmic fashion with respect to the time of rest period. The experiment was continued in normal Tyrode solutions and low; 79 mM, sodium solution which was believed to increase the intracellular calcium possibly by a Na/Ca exchange mechanism across the sarcolemma. The following results were obtained; 1. The disapperance rate of intracellular calcium, expressed as the ratio of contraction amplitude with respect to time of rest period in a normal Tyrode solution, showed fast component within 3 to 5 seconds and slow component after 5 seconds. 2. The contractile amplitude showed and increased according to the decrease of outside Na^+ 105.2±3.48% (Mean±S.E.) in l4OmM, 116.5±2.6% in l2OmM, 162.6±8.8% in 100mM and 191.4±9.1% in 79mM Na^+ respectively. In 40-60mM Na^+ there were no contractions or extrasystole-like one. 3. When outside sodium was lowered to 79 mM, the fast component showed no significant difference with the control one but the slow component showed rather increasing tendency up to 20 seconds and decayed thereafter. The above results could be interpreted as that the intracellular calcium pool was composed of the two fast and slow components and the intracellular calcium was increased, the characteristics of the pool was changed possibly by Na/Ca exchange mechanism in low sodium solution.
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