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 calcium pools in smooth muscle. The current study was designed to investigate the effect of alterations in the extracellular potassium and calcium concentrations, primarily on field-stimulated relaxation of the corpus cavernosum. The results can be summarized as follows: 1. Increasing extracellular calcium at constant potassium mediated a moderate increase in the contractile response to phenylephrine; 2. Increasing extracellular potassium at constant calcium did not affect the contractile response to phenylephrine; 3. Increasing the concentration of extracellular calcium at constant potassium resulted in an increase in field-stimulated 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 prominent at high-frequency stimulation; 5. Increasing the extracellular potassium concentration at constant calcium, or increasing the calcium at constant potassium, had no significant effects on the relaxant effects of ATP and bethanechol; 6. Our findings suggest that, within the corpus cavernosum, neuronal release or synthesis of nitric oxide depends, at least in part, on intracellular bioavailability of calcium.