Distinct regulatory domains on the N‐ and C‐termini of Kv7.4 and Kv7.5 contribute to both their voltage‐dependence of activation and their responses to PKA and PKC.

Abstract

We previously determined that homomeric Kv7.4 potassium channels expressed in smooth muscle cells are insensitive to regulation by protein kinases A and C (PKA or PKC), whereas homomeric Kv7.5 channels are robustly enhanced by PKA and robustly inhibited by PKC activation. To determine the molecular basis for these different responses of Kv7.4 and Kv7.5 channels, using A7r5 vascular smooth muscle cells as an expression system, we examined the regulation of chimeric channels, constructed by inserting subdomains of Kv7.5 into Kv7.4, to determine whether particular parts of Kv7.5 can confer sensitivity onto Kv7.4. A putative PKA phosphorylation site, S53, is located on the N‐terminus of Kv7.5, but is missing from Kv7.4. We found that replacing the Kv7.4 N‐terminus with the Kv7.5 N‐terminus (Q5N‐Q4) rendered Kv7.4 significantly more responsive to a PKA‐activating stimulus than was wild‐type Kv7.4, but this Q5N‐Q4 chimera was still insensitive to AVP (a PKC‐activating stimulus). PKC is thought to target sites on the C‐terminus of Kv7.5, so we switched the C‐terminus of Kv7.4 with that from Kv7.5 (Q5C‐Q4). Preliminary results suggest that this Q5C‐Q4 chimera is sensitive to PKC‐dependent current suppression. The Q5N‐Q4 chimera had voltage‐dependence of activation similar to WT Kv7.4 (V0.5=−31 ± 3 mV for Q5N‐Q4 and −34 ± 2 mV for WT Kv7.4), whereas the Q5C‐Q4 chimera activated at voltages similar to WT Kv7.5 (V0.5=−44 ± 1 mV for Q5C‐Q4 and −45 ± 2 mV for WT Kv7.5). Our findings suggest that distinct regulatory domains on the N‐ and C‐termini of Kv7.5 and Kv7.4 contribute to both the voltage‐dependence of activation and the differential regulation of the channels by protein kinases.Support or Funding InformationThe project described was supported by Award Number I01BX007080 from the Biomedical Laboratory Research & Development Service of the VA Office of Research and Development.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.