EFFECT OF ALTERATION IN THE EXTRACELLULAR POTASSIUM AND CALCIUM ON FIELD-STIMULATED RELAXATION OF THE RABBIT CORPUS CAVERNOSUM

Changes in extracellular potassium or calcium concentration can alter the calcium equilibrium between intracellular and extracellular calciu m pools in smooth muscle. The current study was designed to investigat e the effect of alterations in the extracellular potassium and calcium concentrations, primarily on field stimulated relaxation of the corpu s cavernosum The results can be summarized as follows: 1. Increasing e xtracellular calcium at constant potassium mediated a moderate increas e in the contractile response to phenylephrine; 2. Increasing extracel lular potassium at constant calcium did not affect the contractile res ponse to phenylephrine; 3. Increasing the concentration of extracellul ar calcium at constant potassium resulted in an increase in field-stim ulated relaxation only at low frequency stimulation; 4. Increasing the concentration of extracellular potassium at constant calcium resulted in a marked increase in field-stimulated relaxation, especially promi nent at high-frequency stimulation; 5. Increasing the extracellular po tassium concentration at constant calcium, or increasing the calcium a t constant potassium, had no significant effects on the relaxant effec ts of ATP and bethanechol; 6. Our findings suggest that, within the co rpus cavernosum, neuronal release or synthesis of nitric oxide depends , at least in part, on intracellular bioavailability of calcium.