[Effect of elevated extracellular K+ on the kinetics of alpha 1-adrenergic contractile response in the rat vas deferens].

ABSTRACT

Increase in KCl concentration from 5.5 to 15.5 mM in physiological solution produces potentiation of contractions in response to phenylephrine-mediated by alpha 1-adrenoceptors in the rat vas deferens. The effect of partial depolarisation is dosedependent and reversible. Analysis of the kinetics of adrenergic contractile response to phenylephrine in presence of 15.5 mM KCl shows a decrease of EC50 from 6.63 +/- 0.97 to 3.76 +/- 0.47 microM, i. e. the increase in sensitivity of the organ to agonist. Graphic and mathematic analysis also showed that contractile response to phenylephrine as in control was mediated by a single pool of alpha 1-adrenoceptors without changing the maximum response (Pm) and the Hill coefficient (n). It can be assumed that potentiating effect of hyperpotassium solution upon alpha 1-adrenergic contractions is operated by a mechanism which allows greater recruitment of voltage-operated Ca2+ channels by agonist.