Rescue of cGMP Kinase I Knockout Mice by Smooth Muscle–Specific Expression of Either Isozyme

Smooth muscle expresses the I&agr; and the I&bgr; isoforms of cGMP-dependent protein kinase I (cGKI). Inactivation of the murine cGKI gene prkg1 leads to multiple phenotypes and premature death at ≈6 weeks. We reconstituted mice with the cGKI&agr; or -I&bgr; isozyme to test which isozyme was needed to support basic smooth muscle functions. Mice were generated by gene targeting. The cGKI&agr; or the -I&bgr; coding sequences were placed under the control of the SM22&agr; promoter to express either isoform selectively in smooth muscle cells (SM-I&agr; or SM-I&bgr; transgene). To generate smooth muscle–specific cGKI&agr; or cGKI&bgr; rescue mice, the SM-I&agr; or SM-I&bgr; transgenes were crossed on a cGKI−/− genetic background. The levels of cGKI&agr; or -I&bgr; expression were comparable to endogenous cGKI expression in wild-type aortic and intestinal smooth muscles. In cGKI&agr; or -I&bgr; rescue mice, expression of the isozymes was not detectable in non–smooth muscle tissues and cells. Median survival time of the I&agr; and I&bgr; rescue mice was 52 weeks. Both isozymes mediated the 8-bromo-cGMP–induced relaxation of precontracted jejunum and aorta muscle strips. Activation of both isozymes reduced hormone- or K+-induced [Ca2+]i levels. The cGKI&agr; and cGKI&bgr; rescue mice did not show a significant difference in intestinal passage time of BaSO4 in comparison with wild-type animals. Telemetric blood pressure measurements in conscious freely moving animals did not show differences between rescues and control mice in basal blood pressure and its regulation by DETA-NO, sodium nitroprusside, carbachol, or Y-27632. These results show that cGKI in smooth muscle is essential and that either cGKI isozyme alone can rescue basic vascular and intestinal smooth muscle functions.

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