Abstract
We tested the hypothesis that protein kinase A (PKA) inhibits K2P currents activated by protein kinase C (PKC) in freshly isolated aortic myocytes. PDBu, the PKC agonist, applied extracellularly, increased the amplitude of the K2P currents in the presence of the “cocktail” of K+ channel blockers. Gö 6976 significantly reduced the increase of the K2P currents by PDBu suggesting the involvement of either α or β isoenzymes of PKC. We found that forskolin, or membrane permeable cAMP, did not inhibit K2P currents activated by the PKC. However, when PKA agonists were added prior to PDBu, they produced a strong decrease in the K2P current amplitudes activated by PKC. Inhibition of PDBu-elicited K2P currents by cAMP agonists was not prevented by the treatment of vascular smooth muscle cells with PKA antagonists (H-89 and Rp-cAMPs). Zn2+ and Hg2+ inhibited K2P currents in one population of cells, produced biphasic responses in another population, and increased the amplitude of the PDBu-elicited K+ currents in a third population of myocytes, suggesting expression of several K2P channel types. We found that cAMP agonists inhibited biphasic responses and increase of amplitude of the PDBu-elicited K2P currents produced by Zn2+ and Hg2. 6-Bnz-cAMp produced a significantly altered pH sensitivity of PDBu-elicited K2P-currents, suggesting the inhibition of alkaline-activated K2P-currents. These results indicate that 6-Bnz-cAMP and other cAMP analogs may inhibit K2P currents through a PKA-independent mechanism. cAMP analogs may interact with unidentified proteins involved in K2P channel regulation. This novel cellular mechanism could provide insights into the interplay between PKC and PKA pathways that regulate vascular tone.
Highlights
The aorta has a unique role in the regulation of blood pressure by adjusting to pulsatile flow
We have reported that both adenylate cyclase and phospholipase-C pathways are employed in the G protein-coupled receptor (GPCR) signaling cascades coupled to purinergic receptors in freshly isolated aortic vascular smooth muscle cells (VSMC) [24,25,28]
The important findings of our study are: 1) cAMP agonists did not inhibit K2P currents activated by protein kinase C (PKC); 2) if VSMCs were pretreated with cAMP agonists before PKC activation than they inhibited large fraction of the PDBu-induced K2P currents; 3) cAMP agonists inhibited K2P currents without protein kinase A (PKA) activation; 3) K2P currents inhibited by cAMP agonists were affected by divalent cations and alkaline pH
Summary
The aorta has a unique role in the regulation of blood pressure by adjusting to pulsatile flow. The ratio of the flow pulse amplitude to the mean flow decreases roughly from 6 in the aortic arch to less than 2 in the femoral artery. This mechanism, known as the Windkessel effect, reduces the pulse pressure, the pulse wave velocity, and the hydraulic impedance faced by the heart. The myocyte membrane potential serves as rapid feedback that regulates Ca2+ concentration. It has been suggested that ‘‘leaky’’ K+ channels ( referred to as ‘‘background’’ or ‘‘baseline’’ K+ channels) or two-pore-domain K+ channels (K2P) lack voltage-, time-, or metabolite-dependent inactivation and thereby represent new feedback mechanisms for tuning the resting membrane potential [2,3,4,5,6,7]. K2P channels are divided into subfamilies and are designated by acronyms such as ‘‘Tandem of P domains in weak inward rectifier K+ channel’’ (TWIK) and ‘‘TWIK-related acid-sensitive K+ channel’’ (TASK)
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