Submitted on January 23, 2009
Revised on March 17, 2009
Accepted on April 5, 2009
Cyclic GMP Does Not Activate Two-Pore Domain K Channels in Cerebrovascular Smooth Muscle
Eric E. Lloyd1, Sean P Marrelli1, and Robert M. Bryan, Jr.1*
1 Baylor College of Medicine
* To whom correspondence should be addressed. E-mail: rbryan{at}bcm.tmc.edu.
Two-pore domain K channels (K2P) are a new channel family. The goal of this study was to determine if K2P are activated by the nitric oxide (NO) / cyclic guanosine monophosphate (cGMP) / protein kinase G pathway (PKG) in vascular smooth muscle. Relative levels of message for K2P were assessed in rat middle cerebral arteries (MCAs) using quantitative RT-PCR and K+ currents were measured in freshly dispersed vascular smooth muscle cells of the middle cerebral artery. The rat middle cerebral artery expresses a number of K2P. Message for TREK-1 was the most abundant K2P followed by TASK-1 and TWIK-2 which were expressed at approximately 10% of the level of TREK-1. Message for other K2P was 1% or less than that of TREK-1. A number of the K2P, including TREK-1, TWIK-2, and TASK-1, have putative PKG phosphorylation sites in the intracellular domains. The NO-donor, sodium nitroprusside (SNP, 100 uM), or the membrane permeable analog of cGMP, 8-Br-cGMP (100 µM), elicited transient increases in whole cell current of vascular smooth muscle from rat middle cerebral artery. However, after blocking large conductance Ca-activated K channels (BKCa) with 10 mM TEA, no increase in whole cell current was observed. Since, K2P are resistant to the blocking effects of TEA, we conclude that K2P in vascular smooth muscle was not activated by the NO/cGMP/PKG pathway. Although K2P are highly expressed, K2P currents are not activated via the NO/cGMP pathway in rat MCA smooth muscle, despite the presence of numerous putative PKG phosphorylation sites.
