Effects of some divalent cations on nitrergic relaxations in the mouse corpus cavernosum

Acute effects of some divalent cations (Cd2+, Ni2+, Co2+, Zn2+, Mn2+ and Sn2+) were investigated on neurogenic and endothelium-dependent relaxations in the isolated mouse corpus cavernosum. Neither neurogenic nor endothelium-dependent relaxation was affected by cations at the concentrations used (up to 100 microM), except Cd2+. Although Cd2+ (20 and 40 microM) did not cause any significant alteration in the acetylcholine- (ACh) or sodium nitroprusside- (SNP) induced relaxation, it inhibited electrical field stimulation- (EFS) produced relaxation significantly. Zn2+ and selenium could not reverse this inhibitory action. Cd2+ did block the EFS-evoked guanethidine-sensitive contraction in the presence of N(G)-nitro-L-arginine. Elevation of external Ca2+ content significantly reduced the inhibitions due to Cd2+ on the EFS-induced relaxation and on the EFS-evoked guanethidine-sensitive contraction. In the Ca2+-omitted medium, EFS-induced relaxation disappeared, while acetylcholine-elicited relaxation resisted. Verapamil was ineffective on the relaxation produced by EFS or acetylcholine. However, it significantly diminished phenylephrine-induced contractions. These findings suggest that unlike other cations at the concentrations used in the present study, Cd2+ may have an effect on an external Ca2+-dependent mechanism at the neuronal level, and this effect may be responsible for its acute inhibitory action on the neurogenic relaxation in the mouse corpus cavernosum.