Rescue of cGMP kinase I knockout mice by smooth muscle-specific expression of either isozyme

Smooth muscle expresses the I alpha and the I beta isoforms of cGMP- dependent protein kinase I (cGKI). Inactivation of the murine cGKI gene prkg1 leads to multiple phenotypes and premature death at approximate to 6 weeks. We reconstituted mice with the cGKI alpha or -I beta isozyme to test which isozyme was needed to support basic smooth muscle functions. Mice were generated by gene targeting. The cGKI alpha or the - I beta coding sequences were placed under the control of the SM22 alpha promoter to express either isoform selectively in smooth muscle cells ( SM-I alpha or SM-I beta transgene). To generate smooth muscle-specific cGKI alpha or cGKI beta rescue mice, the SM-I alpha or SM-I beta transgenes were crossed on a cGKI(-/-) genetic background. The levels of cGKI alpha or -I beta expression were comparable to endogenous cGKI expression in wild-type aortic and intestinal smooth muscles. In cGKI alpha or -I beta rescue mice, expression of the isozymes was not detectable in non-smooth muscle tissues and cells. Median survival time of the I alpha and I beta 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 alpha and cGKI beta 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.