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KMID : 0376219930300020131
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Chonnam Medical Journal
1993 Volume.30 No. 2 p.131 ~ p.144
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Contractile Response of Isolated Aorta Through Na+/Ca2+ Exchange System
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Abstract
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Relationship between contractile response induced by external Na+ removal and Na+/Ca2+ exchange system was investigated in ring preparation of thoracic aorta isolated from rats. Replacement of bath fluid with Na+ -free Tris buffer produced the
initial
fast phasic and then sustained tonic contraction of the aortic ring. The Na+ -free contraction was potentiated by increase of external KCI concentration. It was dependent on external Ca2+, and was not inhibited by Phentolamine. Na+ ―free
contraction in
the presence of 21.6 mM KCI was not inhibited by additive treatment with phentolamine and amiloride. However, pretreatment for 20 min with amiloride, benzamil and verapamil attenuated the contraction induced by 21.6mM KCI itself and the Na+
―free
contraction in a concentration-dependent fashion. The potency order on the phasic component of Na+ ―free contraction was amiloridie〉benzamil〉〉verapamil. The inhibitory effect of amiloride was more sensitive to the tonic component than to the
phasic
one. Cyclic GMP contents were not altered in Na+ ―free Tris and KCI 21.6 mM+ Na+ ―free Tris buffer. In hypoxia state, Na+ ―free contraction and PE-induced contraction were markedly inhibited and the former was more sensitive to the hypoxia
than
the
latter. Endothelium-dependent vasorelaxation induced by ACh was sensitively inhibited under hypoxia state.
These results suggest that Na+ ―free contraction in rat thoracic aorta is in part induced through Na+ /Ca+ exchange system is dependent on extracellular Ca2+ and is sensitive to hyposia.
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KEYWORD
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