Submitted on November 7, 2007
Accepted on August 25, 2008
Preservation of cGMP-induced relaxation of pulmonary veins of fetal lambs exposed to chronic high altitude hypoxia: role of PKG and Rho kinase
Yuansheng Gao1*, Ada D Portugal2, Jie Liu2, Sewite Negash2, Weilin Zhou2, Jia Tian2, Ruolan Xiang3, Lawrence D. Longo4, and J. Usha Raj5
1 Los Angeles Biomedical Institute, Harbor-UCLA Medical Center, Torrance, California, United States; Department of Physiology and Pathophysiology, Peking University Health Science Center, Beijing, China
2 Los Angeles Biomedical Institute, Harbor-UCLA Medical Center, Torrance, California, United States
3 Department of Physiology and Pathophysiology, Peking University Health Science Center, Beijing, China
4 Department of Physiology & OB/GYN, Loma Linda University School of Medicine, Loma Linda, California, United States
5 Department of Pediatrics, Geffen School of Medicine at UCLA, Torrance, California, United States
* To whom correspondence should be addressed. E-mail: ysgao{at}labiomed.org.
The roles of Rho kinase (ROCK) and cGMP-dependent protein kinase (PKG) in cGMP-mediated relaxation of fetal pulmonary veins exposed to chronic hypoxia were investigated. Fourth generation pulmonary veins were dissected from near-term fetuses ( 140 days of gestation) delivered from ewes exposed to chronic high altitude hypoxia for ~ 110 days (CH) and from control ewes. After constriction with endothelin-1, 8-Br-cGMP caused a similar relaxation of both control and CH vessels. Rp-8-Br-PET-cGMPS (a PKG inhibitor) inhibited whereas Y-27632 (a ROCK inhibitor) augmented relaxation of control veins to 8-Br-cGMP. These effects were significantly diminished in CH veins. PKG protein expression and activity were greater while ROCK protein expression and activity were less in CH vessels compared to controls. Phosphorylation of threonine 696 (ROCK substrate) and serine 695 (PKG substrate) of the regulatory subunit MYPT1 of myosin light-chain phosphatase was stimulated to a lesser extent in CH than in control veins by endothelin-1 (ROCK stimulant) and 8-Br-cGMP (PKG stimulant), respectively. The phosphorylation and dephosphorylation of myosin light-chain (MLC) caused by endothelin-1 and 8-Br-cGMP, respectively, were less in CH veins than in controls. These results suggest that chronic hypoxia in utero upregulates PKG activity but attenuates PKG action in fetal pulmonary veins. These effects are offset by the diminished ROCK action on MYPT1 and MLC and thus lead to an unaltered response to cGMP.
