Submitted on July 19, 2007
Accepted on January 3, 2008
Heme Oxygenase-1 Induction Depletes Heme and Attenuates Pulmonary Artery Relaxation and Guanylate Cyclase Activation by Nitric Oxide
Christopher J Mingone1, Mansoor Ahmad1, Sachin A Gupte1, Joseph L Chow1, and Michael S. Wolin1*
1 Physiology, New York Medical College, Valhalla, New York, United States
* To whom correspondence should be addressed. E-mail: mike_wolin{at}nymc.edu.
This study examines in endothelium-denuded bovine pulmonary arteries the effects of increasing heme oxygenase-1 (HO-1) activity on relaxation and soluble guanylate cyclase (sGC) activation by nitric oxide (NO). A 24 hour organ culture with 0.1 mM cobalt chloride (CoCl2) or 30 µM Co-protoporphyrin IX was developed as a method of increasing HO-1 expression. These treatments increased HO-1 expression and HO activity by ~2-4 fold, and lowered heme levels by 40-45%. Induction of HO-1 was associated with an attenuation of pulmonary arterial relaxation to the NO-donor spermine-NONOate. The presence of a HO-1 inhibitor 30 µM chromium mesoporphyrin during the 24 hour organ culture (but, not acute treatment with this agent) reversed the attenuation of relaxation to NO seen in arteries co-cultured with agents that increased HO-1. Relaxation to isoproterenol, which is thought to be mediated through cAMP, was not altered in arteries with increased HO-1. Inducers of HO-1 did not appear to alter basal sGC activity in arterial homogenates or expression of the 
1-subunit of sGC. However, the increase in activity seen in the presence of 1 µM spermine-NONOate was attenuated in homogenates obtained from arteries with increased HO-1. Since arteries with increased HO-1 had decreased levels of superoxide detected by the chemiluminescence of 5 µM lucigenin, superoxide did not appear to be mediating the attenuation of relaxation to NO. These data suggest that increasing HO-1 activity depletes heme, and this is associated with an attenuation of pulmonary artery relaxation and sGC activation responses to NO.
