Presence of cyclic nucleotide-gated channels in the rat urethra and their involvement in nerve-mediated nitrergic relaxation

Abstract

We have addressed the distribution of cGMP-gated channels (CNG) in the rat urethra for the first time, as well as their putative role in mediating of the relaxation elicited by electrical field stimulation of nitrergic nerves. Functional studies have shown that specifically blocking CNG with L-cis-diltiazem leads to the rapid inhibition of urethral relaxation induced either by nitric oxide (NO) released by the nerves or by soluble guanylate cyclase activated with YC-1. By contrast, nerve-mediated noradrenergic contractions were only slowly and mildly reduced by L-cis-diltiazem. This effect was mimicked by lower concentrations of the D-diltiazem isomer, probably due to the nonspecific inhibition of voltage-dependent calcium channels. However, D-diltiazem did not affect relaxation responses. The expression of heteromeric retinal-like CNGA1 channels was demonstrated by conventional PCR on mRNA from the rat urethra. These channels were located in a subpopulation of intramuscular interstitial cells of Cajal (ICC) as well as in smooth muscle cells, although they were less abundant in the latter. CNG channels could not be visualized in any nervous structure within the urethral wall, in agreement with the emerging view that a subset of ICC serves as a target for NO. These channels could provide a suitable ionic mechanism to associate the changes in cytosolic calcium with the activation of the nitric NO-cGMP pathway and relaxation although the precise mechanisms involved remain to be elucidated.