cGMP does not activate two-pore domain K+ channels in cerebrovascular smooth muscle

Lloyd EE, Marrelli SP, Bryan RM Jr. cGMP does not activate two-pore domain K+ channels in cerebrovascular smooth muscle. Am J Physiol Heart Circ Physiol 296: H1774-H1780, 2009. First published April 10, 2009; doi:10.1152/ajpheart.00082.2009.-Twopore domain K+ (K-2P) channels are a new channel family. The goal of this study was to determine if K-2P channels are activated by the nitric oxide (NO)/cGMP/PKG pathway in vascular smooth muscle. Relative levels of message for K-2P channels 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 MCA. The rat MCA expresses a number of K-2P channels. Message for TREK-1 was the most abundant K-2P channel, followed by TASK-1 and TWIK-2, which were expressed at similar to 10% of the level of TREK-1. Message for other K-2P channels was 1% or less than that of TREK-1. A number of K-2P channels, including TREK-1, TWIK-2, and TASK- 1, have putative PKG phosphorylation sites in the intracellular domains. The NO donor sodium nitroprusside (100 mu M) or the membrane permeable analog of cGMP 8-bromo-cGMP (10 mu M) elicited transient increases in whole cell current of vascular smooth muscle from the rat MCA. However, after large-conductance Ca2+-activated K+ channels had been blocked with 10 mM tetraethylammonium (TEA), no increase in whole cell current was observed. Since K-2P channels are resistant to the blocking effects of TEA, we conclude that K-2P channels in vascular smooth muscle were not activated by the NO/cGMP/PKG pathway. Although K-2P channels are highly expressed, K-2P currents are not activated via the NO/cGMP pathway in rat MCA smooth muscle, despite the presence of numerous putative PKG phosphorylation sites.