Expression of penile neuronal nitric oxide synthase variants in the rat and mouse penile nerves

Penile erection is mediated by nitric oxide (NO) synthesized by the neurona l nitric oxide synthase (nNOS). In the rat penis, the main nNOS mRNA varian t, PnNOS, differs from cerebellar nNOS (CnNOS) by a 102 base pair insert en coding a 34-amino acid sequence, In the mouse, two nNOS mRNAs have been ide ntified: nNOS alpha, encoding a 155-kDa protein, and an exon 2-deletion var iant, nNOS beta, encoding a 135-kDa protein that lacks a domain where a pro tein inhibitor of nNOS (PIN) binds. We wished to determine whether PnNOS al pha and beta are expressed in the rat penis and are located in the nerves a nd whether the beta form persists in the potent nNOS knock-out mouse (nNOS( Delta Delta)). A PnNOS antibody against the insert common to both PnNOS alp ha and beta detected the expected 155-kDa protein in PnNOS alpha-transfecte d cells. This antibody, and the one common to PnNOS/CnNOS, showed (on Weste rn blots) the 155- and 135-kDa nNOS variants in rat penile tissue during de velopment and aging. PnNOS alpha mRNA and its subvariants were found as the main nNOS in the penile corpora, the cavernosal nerve, and the pelvic gang lia, with lower levels of PnNOS beta mRNA. In tissue sections, PnNOS protei n was immunodetected in the penile nerve endings in the rat and in the nNOS wild-type and nNOS(Delta Delta) mice. An antibody against the sequence enc oded by exon 2 did not react (on Western blots) with the 135-kDa band, whic h confirms that this protein is the beta form. In conclusion, both PnNOS al pha and beta are expressed in the rat penis at all ages and are located in the nerves, The beta form may allow nitric oxide synthesis during erection to be partially insensitive to PIN. The residual expression of PnNOS, and p ossibly CnNOS, in the penis of the nNOS(Delta Delta) mouse occurs through t ranscription of the beta mRNA, and this may explain the retention of erecti le function when the expression of nNOS alpha is disrupted.