Kv7.5 Potassium Channel Subunits are the Primary Target for PKA-Dependent Enhancement of Vascular Smooth Muscle Kv7 Currents

Lyubov I Brueggemann,Bharath K Mani,Christina Robakowski,Leanne L Cribbs,Kenneth L Byron

doi:10.1016/j.bpj.2015.11.3242

Lyubov I Brueggemann, Bharath K Mani + Show 3 more

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https://doi.org/10.1016/j.bpj.2015.11.3242

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Abstract

Kv7 (KCNQ) channels, formed as homo- or hetero-tetramers of Kv7.4 and Kv7.5 α-subunits, are important regulators of vascular smooth muscle cell (VSMC) membrane voltage. Recent studies demonstrate that direct pharmacological modulation of VSMC Kv7 channel activity can influence blood vessel contractility and diameter. However, physiological regulation of Kv7 channel activity is still poorly understood. Here, we measure the effect of cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) activation on whole cell K+ currents through endogenous Kv7.5 channels in A7r5 rat aortic smooth muscle cells, or through Kv7.4/Kv7.5 heteromeric channels natively expressed in rat mesenteric artery smooth muscle cells. The contributions of specific α-subunits are further dissected using exogenously expressed human Kv7.4 and Kv7.5 homo- or hetero-tetrameric channels in A7r5 cells. Stimulation of Gs-coupled β-adrenergic receptors with isoproterenol induced PKA-dependent activation of endogenous Kv7.5 currents in A7r5 cells. The receptor-mediated enhancement of Kv7.5 currents was mimicked by pharmacological agents that increase [cAMP] (forskolin, rolipram, 3-isobutyl-1-methylxanthine, and papaverine) or mimic cAMP (8-bromo-cAMP); the 2- to 4-fold PKA-dependent enhancement of currents was also observed with exogenously expressed Kv7.5 channels. In contrast, exogenously expressed hetero-tetrameric Kv7.4/7.5 channels in A7r5 cells or native mesenteric artery smooth muscle Kv7.4/7.5 channels were only modestly enhanced, and homo-tetrameric Kv7.4 channels were almost entirely insensitive to this regulatory pathway. There results suggest that signal transduction mediated responsiveness of Kv7 channel subunits to cAMP/PKA activation follows the order of Kv7.5>>Kv7.4/Kv7.5>Kv7.4 and that physiological or pathological alteration of subunit stoichiometry of Kv7 channels would determine their responsiveness to the cAMP/PKA pathway.

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