Protein Kinase C-Dependent Modulation of Heterologously Expressed Homomeric Kv7.4, Kv7.5 and Heteromeric Kv7.4/7.5; Differential Sensitivities to Low Concentrations of Vasopressin and PMA in A7R5 Vascular Smooth Muscle Cells

Abstract

Kv7.4 and Kv7.5 voltage-activated potassium channels are proposed to contribute to the maintenance of resting membrane voltage in smooth muscle cells. We had previously provided evidence that Kv7.4 and Kv7.5 form predominantly heteromeric channels when natively or exogenously expressed in vascular smooth muscle cells. Endogenous Kv7 currents in smooth muscle cells are suppressed upon activation of Gq coupled receptors. It remained to be elucidated if both Kv7.4 and Kv7.5 respond similarly to low concentrations of vasopressin (AVP), an agonist of the V1a Gq-coupled receptor. using patch-clamp techniques, we measured currents through human Kv7.4 and Kv7.5 channels expressed individually or together in A7r5 rat aortic smooth muscle cells and compared their sensitivity to AVP (100 pM and 500 pM) and to the protein kinase C (PKC) activator phorbol 12-myristate 13-acetate (PMA, 1nM). AVP (100 pM) and PMA suppressed currents through Kv7.4, Kv7.5 and Kv7.5/7.5. Currents were reduced with different voltage dependencies and potencies in the rank order: Kv7.5 > Kv7.4/7.5 > Kv7.4. Both AVP and PMA increased the steepness of Kv7.5 voltage-dependent activation and dramatically decreased Gmax. In contrast, AVP and PMA induced a rightward shift of the Kv7.4 activation curve with only a slight reduction in maximal conductance (Gmax). The modulation of Kv7.4/7.5 activation by AVP and PMA had intermediate biophysical characteristics that were distinct from the modulation of either of the homomeric configurations. These findings reinforce the significance of PKC-dependent regulation of the Kv7 channels and suggest a differential regulation of Kv7.4 and Kv7.5 channel subunits by PKC-dependent phosphorylation.