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KMID : 0365819830230010179
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Journal of Pusan Medical College
1983 Volume.23 No. 1 p.179 ~ p.188
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Effect of Ca^(2+) and Na^(+) on Contraction Induced by Na-free Solution in Na-loaded Ileum of Cat
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Abstract
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The possibility of involvement of a Na-Ca exchange mechanism in the contractile responses induced by Na-free solution was studied in isolated cat ileum. Na-loaded tissues were prepared by pretreating them with ouabain(2 x 10´5M) for 3 h and then were exposed to Na-free sucrose solution.
1. Na-free solution caused more rapid and larger contractions in Na-loaded tissues than in normaltissues.
2. The contraction by Na-free solution in Na-loaded tissues was unaffected by verapamil ( 4 jug/ml) and atropine(l0"6M). These drugs inhibited mostly and 20% the contraction by 80 mM-KC1 in normal tissues, respectively. La´*(5 mM) inhibited partially the contraction by Na-free solution in Na-loading tissues.
3. The magnitude of the contraction induced by Na-free solution in Na-loaded tissues was dependent on the concentration of external Ca´*.
4. When the contraction was induced by varying (Na), solution in Na-loaded tissues, the magnitude of the contraction increased as the concentration of Na in the exposed solution decreased.
5. When the tissues were incubated with ouabain(2xl0-6M) for 3 h, cellular Na content was linear with the concentration of Na in the Na-loading solution. The magnitude of the contractions induced by Na-free solution in these muscles was dependent on the cellular Na content.
These results suggest that the contraction induced by Na-free solution is caused by Ca-influx which is dependent on internal Na, supporting some form of Na-Ca exchange mechanism operating in the cat ileum which is not blocked by verapamil but partially by La´*
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