Submitted on December 28, 2005
Accepted on March 7, 2006
Evidence for Two-Pore Domain Potassium Channels in Rat Cerebral Arteries
Robert M Bryan1*, Junping You1, Sharon C Phillips1, Jon J Andresen1, Eric E Lloyd1, Paul A Rogers1, Stuart E. Dryer1, and Sean P Marrelli1
1 Anesthesiology, Baylor College of Medicine, Houston, Texas, United States; Medicine (Cardiovascular Sciences), Baylor College of Medicine, Houston, Texas, United States; Molecular Physiology & Biophysics, Baylor College of Medicine, Houston, Texas, United States; Physiology, Louisiana State University School of Medicine, New Orleans, Louisiana, United States; Biochemistry and Biological Sciences, University of Houston, Houston, Texas, United States
* To whom correspondence should be addressed. E-mail: rbryan{at}bcm.edu.
Little is known about the presence and function of two-pore domain K channels (K2P in vascular smooth muscle cells. Five members of the K2P family are known to be directly activated by arachidonic acid (AA). The purpose of this study was to determine (a) if AA-sensitive K2P are expressed in cerebral vascular smooth muscle cells and (b) if AA dilates the rat middle cerebral artery (MCA) by increasing K+ currents in vascular smooth muscle cells via an atypical K channel. RT-PCR revealed message for the AA-sensitive K2P channels, TREK-1, TREK-2, TRAAK, THIK-1, and TWIK-2 in rat MCA. However, in isolated vascular smooth muscle cells, only message for TWIK-2 was found. Western blotting showed that TWIK-2 is present in MCA and immunohistochemistry further demonstrated that it was present in vascular smooth muscle cells. AA (10-100 µM) dilated MCAs through a mechanism independent of endothelium. The dilation to AA was not affected by inhibiting cyclooxygenase, epoxygenase, or lipoxygenase, or by inhibition of classic K channels using TEA, 4AP, gilbenclamide, or Ba2+. The dilations to AA were blocked by 50 mM K+, indicating involvement of a K channel. AA (10 µM) increased whole cell K+ currents in dispersed cerebral vascular smooth muscle cells. The AA-induced currents were not affected by inhibitors of the AA metabolic pathways or blockade of classical K channels. We conclude that AA dilates the rat MCA and increases K+ currents in vascular smooth muscle cells via an atypical K channel, which is likely a member of the K2P family.
