Oxyhemoglobin-induced expression of R-type Ca2+ channels in cerebral arteries.
OBJECTIVE
Cerebral vasospasm after subarachnoid hemorrhage (SAH) is a major contributor to mortality and morbidity after aneurysm rupture. Recently, R-type voltage-dependent Ca(2+) channel (VDCC) expression has been associated with increased cerebral artery constriction in a rabbit model of SAH. The goal of the present study was to examine whether the blood component oxyhemoglobin (oxyHb) can mimic the ability of SAH to cause R-type VDCC expression in the cerebral vasculature.


METHODS
Rabbit cerebral arteries were organ cultured in serum-free media for up to 5 days in the presence or absence of purified oxyHb (10 micromol/L). Diameter changes in response to diltiazem, (L-type VDCC antagonist) and SNX-482 (R-type VDCC antagonist) were recorded at day 1, 3, or 5 in arteries constricted by elevated extracellular potassium. RT-PCR was performed on RNA extracted from arteries cultured for 5 days (+/-oxyHb) to assess VDCC expression.


RESULTS
After 5 days, oxyHb-treated arteries were less sensitive and partially resistant to diltiazem compared to similar arteries organ cultured in the absence of oxyHb. Further, SNX-482 dilated arteries organ cultured for 5 days in the presence, but not in the absence, of oxyHb. RT-PCR revealed that oxyHb treated arteries expressed R-type VDCCs (Ca(V) 2.3) in addition to L-type VDCCs (Ca(V) 1.2), whereas untreated arteries expressed only Ca(V) 1.2.


CONCLUSIONS
These results demonstrate that oxyhemoglobin exposure for 5 days induces the expression of Ca(V) 2.3 in cerebral arteries. We propose that oxyhemoglobin contributes to enhanced cerebral artery constriction after SAH via the emergence of R-type VDCCs.
Link
Timothy E
TE
Department of Pharmacology, University of Vermont College of Medicine, 86 Beaumont Ave, Burlington, VT 05405, USA.
Murakami
Kentaro
K
Beem-Miller
Micah
M
Tranmer
Bruce I
BI
Wellman
George C
GC
D000783:Aneurysm / Q000378:metabolism; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D002536:Cerebral Arteries / Q000378:metabolism*; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D004730:Endothelium, Vascular / Q000378:metabolism; D005786:Gene Expression Regulation; D008297:Male; D009130:Muscle, Smooth / Q000378:metabolism; D010108:Oxyhemoglobins / Q000096:biosynthesis*; D011817:Rabbits; D013345:Subarachnoid Hemorrhage / Q000378:metabolism
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D016895:Culture Media, Serum-Free; D010108:Oxyhemoglobins; D004110:Diltiazem