Spare guanylyl cyclase NO receptors ensure high NO sensitivity in the vascular system

Abstract

In the vascular system, the receptor for the signaling molecule NO, guanylyl cyclase (GC), mediates smooth muscle relaxation and inhibition of platelet aggregation by increasing intracellular cyclic GMP (cGMP) concentration. The heterodimeric GC exists in 2 isoforms (a 1 -GC, a 2 -GC) with indistinguishable regulatory properties. Here, we used mice deficient in either a 1 -or a 2 -GC to dissect their biological functions. In platelets, a 1 -GC, the only isoform present, was responsible for NO-induced inhibition of aggregation. In aortic tissue, a 1 -GC, as the major isoform (94%), mediated vasodilation. Unexpectedly, a 2 -GC, representing only 6% of the total GC content in WT, also completely relaxed a 1 -deficient vessels albeit higher NO concentrations were needed. The functional impact of the low cGMP levels produced by a 2 -GC in vivo was underlined by pronounced blood pressure increases upon NO synthase inhibition. As a fractional amount of GC was sufficient to mediate vasorelaxation at higher NO concentrations, we conclude that the majority of NO-sensitive GC is not required for cGMP-forming activity but as NO receptor reserve to increase sensitivity toward the labile messenger NO in vivo.

Disruption of Guanylyl Cyclase-G Protects against Acute Renal Injury

“…29,30 In addition, the cGMP level may dynamically change during the activation process, and local subcellular effects caused by compartmentalization of GC-G may not be detected by measurement of whole-organ content. Alternatively, the disconnection between renal cGMP level and renal I/R injury seen in Figures 3 and 8 suggests that a cGMP-independent function of GC-G may be important for renal I/R pathophysiology.…”

Long-Term Potentiation in the Visual Cortex Requires Both Nitric Oxide Receptor Guanylyl Cyclases

“…Isoform-deficient KO mice were generated by deleting either one of the ␣ subunits. Both strains (␣ 1 -KO, ␣ 2 -KO) do not show any reduction of life expectancy or obvious behavioral abnormalities (Mergia et al, 2006). Western blot analysis of the GC subunits in the brain of WT and KO mice confirmed the lack of the ␣ 1 or ␣ 2 subunit in the respective KO strain (Fig.…”

“…Generation and genotyping of the ␣ 1 -or ␣ 2 -KO mice has been described previously by Mergia et al (2006). Briefly, exon 4 of the ␣ 1 or ␣ 2 subunits floxed by loxP-sites (␣ 1 ϩ/flox and ␣ 2 ϩ/flox ) were removed by crossing with the general deleter mouse EIIa-Cre, respectively.…”

“…Brains or visual cortex were removed after decapitation and homogenized immediately in buffer (50 mM triethanolamine/HCl, 50 mM NaCl,1 mM EDTA, 2 mM DTT, 0.2 M benzamidine, 0.5 M PMSF, and 1 M pepstatin A, pH 7.4, 4°C). After centrifugation (800 ϫ g, 5 min, 4°C), homogenates were subjected to Western blot analysis performed as described previously by Mergia et al (2006). The protein concentration was determined in triplicates and repeated three times (Bradford; Bio-Rad, Hercules, CA).…”

“…Homogenates obtained as described above were used to measure NO-stimulated cGMP-forming activities as described by Mergia et al (2006).…”