ABSTRACT
PURPOSE: Soluble guanylyl cyclase (sGC), which plays a pivotal role in penile erection, is a heterodimer build up by an α and a ß subunit. For both subunits two isoforms have been characterized, but only the sGCα(1)ß(1) and sGCα(2)ß(1) isoforms seem to be functionally active. To elucidate the functional role of the sGCα(1)ß(1) heterodimer in the mechanism of erection, experiments were performed in vivo and on isolated corpora cavernosa (CC) using sGCα(1)(-/-) mice. MATERIALS AND METHODS: For the in vivo study sGC-dependent and -independent vasorelaxing agents were injected intracavernosally in sGCα(1)(-/-) and sGCα(1)(+/+) mice and the rise in intracavernosal pressure was recorded. For the in vitro study, isolated CC tissues from sGCα(1)(-/-) and sGCα(1)(+/+) mice were mounted in organ baths for isometric tension recording and concentration-dependent curves were obtained for sGC-dependent and -independent vasorelaxing agents. These experiments were performed on 2 different mice strains (129SvEvS7 and C57BL6/J) to determine potential strain differences. RESULTS: The responses in sGCα(1)(-/-) after administration of the NO-donors, sodium nitroprusside (SNP) and spermine-NO, and to electrical stimulation are significantly reduced although not completely abolished. Responses to sGC-independent vasorelaxing agents are similar in sGCα(1)(-/-) and sGCα(1)(+/+) mice from both strains suggesting that the decreased potential of smooth muscle relaxation is not related to structural changes or changes in the pathway downstream sGC. CONCLUSION: This study illustrates the strain-independent importance of the sGCα(1)ß(1) heterodimer, although remaining vasorelaxing responses in the sGCα(1)(-/-) mice suggest a complementary role for the sGCα(2)ß(1) isoform or (an) sGC-independent mechanism(s).
Subject(s)
Guanylate Cyclase/physiology , Penile Erection/physiology , Receptors, Cytoplasmic and Nuclear/physiology , Vasodilation/physiology , Animals , Colforsin/pharmacology , Electric Stimulation , Guanylate Cyclase/genetics , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Models, Animal , Nitric Oxide Donors/pharmacology , Nitroprusside/pharmacology , Penile Erection/drug effects , Receptors, Cytoplasmic and Nuclear/genetics , Soluble Guanylyl Cyclase , Spermine/analogs & derivatives , Spermine/pharmacologyABSTRACT
OBJECTIVE: Soluble guanylyl cyclase (sGC), the predominant receptor for nitric oxide (NO), exists in 2 active isoforms (alpha(2)beta(1) and alpha(1)beta(1)). In vascular tissue sGCalpha(1)beta(1) is believed to be the most important. The aim of our study was to investigate the functional importance of the sGCalpha(1)-subunit in vasorelaxation. METHODS: Aortic and femoral artery segments from male and/or female sGCalpha(1)(-/-) mice and wild-type littermates were mounted in a small-vessel myograph for isometric tension recording. This was supplemented with biochemical measurements of the cGMP concentration and sGC enzyme activity. RESULTS: The functional importance of sGCalpha(1)beta(1) was demonstrated by the significantly decreased relaxing effects of acetylcholine (ACh), sodium nitroprusside (SNP), S-nitroso-N-acetylpenicillamine (SNAP), NO gas, YC-1, BAY 41-2272 and T-1032 in the sGCalpha(1)(-/-) mice of both genders. Moreover, the basal and SNP-stimulated cGMP levels and basal sGC activity were significantly lower in the sGCalpha(1)(-/-) mice. However, the relaxing effects of NO, BAY 41-2272 and YC-1 seen in blood vessels from sGCalpha(1)(-/-) mice indicate a role for an sGCalpha(1)beta(1)-independent mechanism. The increase in sGC activity after addition of BAY 41-2272 and the inhibition of the ACh-, SNP-, SNAP- and NO gas-induced response by the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) in the sGCalpha(1)(-/-) mice are observations suggesting that the sGCalpha(2)beta(1) isoform is also functionally active. However, the insignificant increase in cGMP in response to SNP and the non-upregulated sGCalpha(2) expression level in the sGCalpha(1)(-/-) mice suggest rather the involvement of (an) sGC-independent mechanism(s). CONCLUSIONS: We conclude that sGCalpha(1)beta(1) is involved in the vasorelaxation induced by NO-dependent and NO-independent sGC activators in both genders. However, the remaining relaxation seen in the sGCalpha(1)(-/-) mice suggests that besides sGCalpha(1)beta(1) also the minor isoform sGCalpha(2)beta(1) and/or (an) sGC-independent mechanism(s) play(s) a substantial role.
