Submitted on March 14, 2008
Accepted on May 16, 2008
Role of heme oxygenase-2 in pial arteriolar response to acetylcholine in mice with and without transfusion of cell-free hemoglobin polymers
Xinyue Qin1, Herman Kwansa1, Enrico Bucci2, Sylvain Dore1, Darren Boehning3, David Shugar4, and Raymond C. Koehler1*
1 Dept. of Anesthesiology & Critical Care Med., Johns Hopkins Medical Institutions, Baltimore, Maryland, United States
2 Dept. of Biochemistry and Molecular Biology, University of Maryland School of Medical, Baltimore, Maryland, United States
3 Dept. of Neuroscience, Johns Hopkins Medical Institutions, Baltimore, Maryland, United States
4 Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Warsaw, Poland
* To whom correspondence should be addressed. E-mail: rkoehler{at}jhmi.edu.
Carbon monoxide derived from heme oxygenase (HO) may participate in cerebrovascular regulation under specific circumstances. Previous work has shown that HO contributes to feline pial arteriolar dilation to acetylcholine after transfusion of a cell-free polymeric hemoglobin oxygen carrier. The role of constitutive HO2 in the pial arteriolar dilatory response to acetylcholine was determined by using 1) HO2 null mice (HO2-/-), 2) the HO inhibitor tin protoporphyrin IX (SnPPIX), and 3) 4,5,6,7-tetrabromobenzotriazole (TBB), an inhibitor of CK2-dependent phosphorylation of HO2. In anesthetized mice, superfusion of a cranial window with SnPPIX decreased arteriolar dilation produced by 10 µM acetylcholine by 51%. After partial polymeric hemoglobin exchange transfusion, the acetylcholine response was normal but was reduced 72% by SnPPIX and 95% by TBB. In HO2-/- mice, the acetylcholine response was modestly reduced by 14% compared to control mice and was unaffected by SnPPIX. After hemoglobin transfusion in HO2-/- mice, acetylcholine responses were also unaffected by SnPPIX and TBB. In contrast, nitric oxide (NO) synthase inhibition completely blocked the acetylcholine responses in hemoglobin-transfused HO2-/- mice. We conclude 1) that HO2 activity partially contributes to acetylcholine-induced pial arteriolar dilation in mice, 2) that this contribution is augmented in the presence of a plasma-based hemoglobin polymer and appears to depend on a CK2 kinase mechanism, 3) that NO synthase activity rather than HO1 activity contributes to the acetylcholine reactivity in HO2-/- mice, and 4) that plasma-based polymeric hemoglobin does not scavenge all of the NO generated by cerebrovascular acetylcholine stimulation.
