Interaction between XXXX and @entity3884 ions in @entity235 coronary arteries.

@entity5838 @entity308 @entity3884 @entity235 @entity594 @entity3157 @entity520 @entity460 @entity972 @entity141
In vitro experiments were carried out to study the effects of "respiratory" and "metabolic" acid-base alterations on @entity235 coronary arteries precontracted by high @entity972 . @entity5838 (pH 7.70 +/- 0.02) increased the coronary tone by 33 +/- 3% (P less than 0.05) and @entity520 (pH 7.10 +/- 0.01) decreased it by 30 +/- 3% (P less than 0.05). The tension stabilized in approximately 15 mins and its variation was of similar extent whether changes in extracellular pH were produced by changes in PCO2 or in @entity3157 concentration. The contractile changes were not abolished neither by alpha or beta adrenergic blockade nor by endothelium denudation. The effect of pH could not be offset by altering extracellular @entity972 or @entity460 when the plateau of the relationship between contractility of the smooth muscle and concentration of these ions was reached. When tonus developed by the strips and [Ca2+]0 were plotted reciprocally, DTmax significantly increased in @entity5838 and decreased in @entity520 . No significant changes in Ca50 ([ @entity141 ]0 necessary to obtain 50% of maximal force) were detected. pH changes did not modify @entity141 influx but a relaxation of similar extent induced by @entity594 produced a detectable decrease in @entity141 influx. @entity141 efflux was augmented in @entity520 and @entity308 in @entity5838 . Our data do not support the hypothesis of @entity3884 ion changes inducing @entity460 influx alterations in a competitive fashion as the mechanism involved to contract or relax conduit coronary arteries. On the contrary, they suggest that acid-base variations alter the contractile activity of vascular smooth muscle by modulating @entity141 efflux.
