Importance of @entity1760 and @entity972 concentration on basal tone and XXXX -induced contractions in @entity235 isolated coronary artery.

@entity1169 @entity4444 @entity3933 @entity455 @entity1025 @entity235 @entity141 @entity5521 @entity3009 @entity750 @entity972 @entity3897 @entity1760
1. In vitro studies were undertaken to investigate the effects of external @entity972 ([K+]o) and @entity1760 ([ @entity1025 ]o) concentration on @entity235 coronary arterial basal tone and on @entity750 ( @entity750 )-induced contractions. 2. Acute withdrawal of, or reduction in, [K+]o produced relaxation of basal tone in isolated coronary arteries, whereas acute withdrawal (but not reduction) of [ @entity1025 ]o produced contraction of these blood vessels. 3. The magnitude of coronary contraction obtained on withdrawal of [ @entity1025 ]o was dependent upon the [K+]o; the higher the [K+]o, the greater the contraction. 4. The precise ratio of [K+]o/[ @entity1025 ]o appeared to be important in dictating the degree of contraction (maximum response) and sensitivity (EC50) of @entity235 coronary vascular smooth muscle cells to @entity750 . The EC50 to @entity750 was enhanced by increases in the [K+]o/[ @entity1025 ]o ratio, whereas the ability of @entity750 to induce a maximal contraction was attenuated by decreases in the [K+]o; the latter being modulated by [ @entity1025 ]o. Small changes in [ @entity1025 ]o could effect large changes in the EC50 as [K+]o was lowered. 5. These actions took place over patho-physiological ranges of [K+]o and [ @entity1025 ]o. 6. Maintenance of a constant [K+]o/[ @entity1025 ]o ratio, irrespective of the exact [K+]o and [ @entity1025 ]o, produced similar degrees of maximum tension. 7. Use of intact @entity455 preparations and helically-cut vascular strips produced similar results with varying [K+]o/[ @entity1025 ]o. 8. A variety of pharmacological receptor antagonists ( @entity5521 , @entity1169 , @entity3897 , @entity3933 , @entity4444 ), as well as a @entity3009 cyclo-oxygenase inhibitor, did not modify the altered contractile responses or basal tone evoked by varying [K+]o/[ @entity1025 ]o ratios. 9. These results suggest: (1) that basal tone and contractility of @entity235 coronary vascular smooth muscle cells appear to be exquisitely sensitive to alterations in extracellular K+ and @entity1025 ; and (2) @entity750 receptor-operated @entity141 channels, as well as those @entity141 channels involved in generation of coronary arterial basal tone are modulated and controlled by the precise concentrations of [K+]o and [ @entity1025 ]o.
