PT - JOURNAL ARTICLE AU - Lyubov I. Brueggemann AU - Leanne L. Cribbs AU - Kenneth L. Byron TI - Structural determinants of Kv7.5 potassium channels that confer changes in phosphatidylinositol 4,5-bisphosphate (PIP2) affinity and signaling sensitivities in smooth muscle cells AID - 10.1124/mol.119.117192 DP - 2019 Jan 01 TA - Molecular Pharmacology PG - mol.119.117192 4099 - http://molpharm.aspetjournals.org/content/early/2019/12/23/mol.119.117192.short 4100 - http://molpharm.aspetjournals.org/content/early/2019/12/23/mol.119.117192.full AB - Smooth muscle cells express Kv7.4 and Kv7.5 voltage-dependent potassium channels, which have each been implicated as regulators of smooth muscle contractility, though they display different sensitivities to signaling via cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and protein kinase C (PKC). We expressed chimeric channels composed of different components of the Kv7.4 and Kv7.5 α-subunits in vascular smooth muscle cells to determine which components are essential for enhancement or inhibition of channel activity. Forskolin, an activator of the cAMP/PKA pathway, increased wild-type Kv7.5, but not wild-type Kv7.4 current amplitude. Replacing the amino-terminus of Kv7.4 with the amino-terminus of Kv7.5 conferred partial responsiveness to forskolin. In contrast, swapping carboxy-terminal phosphatidylinositol 4,5-bisphosphate (PIP2) binding domains, or the entire C-terminus, was without effect on the forskolin response, but the latter conferred responsiveness to arginine-vasopressin (an inhibitory PKC-dependent response). Serine-to-alanine mutation at position 53 of the Kv7.5 amino-terminus abrogated its ability to confer forskolin sensitivity to Kv7.4. Forskolin treatment reduced the sensitivity of Kv7.5 channels to Ci-VSP-induced PIP2 depletion, whereas activation of PKC with phorbol-12-myristate-13-acetate potentiated the Ci-VSP-induced decline in Kv7.5 current amplitude. Our findings suggest that PKA-dependent phosphorylation of serine 53 on the amino-terminus of Kv7.5 increases its affinity for PIP2, while PKC-dependent phosphorylation of the Kv7.5 carboxy-terminus is associated with a reduction in PIP2 affinity; these changes in PIP2 affinity have corresponding effects on channel activity. Resting affinities for PIP2 differ for Kv7.4 and Kv7.5, based on differential responsiveness to Ci-VSP activation and different rates of current rundown in ruptured patch recordings.SIGNIFICANCE STATEMENT Kv7.4 and Kv7.5 channels have been identified as signal transduction intermediates and drug targets for the control of smooth muscle tone. The present studies identify distinct functional domains that are responsible for differential sensitivities of Kv7.4 and Kv7.5 to stimulatory and inhibitory signaling, and reveal structural features of the channel subunits that determine their biophysical properties. These findings may improve our understanding of the roles of these channels in smooth muscle physiology and disease, particularly in conditions where Kv7.4 and Kv7.5 are differentially expressed.