Diclofenac Activates Kv7.4 and Inhibits Kv7.5 Potassium Channels Heterologously Expressed in A7r5 Vascular Smooth Muscle Cells

Abstract

Members of the KCNQ (Kv7) voltage-gated potassium channel gene family are differentially expressed through the body. Five Kv7 subtypes play major roles in regulation of membrane potential and cell excitability within different tissues. Well known functions of Kv7.1 in cardiac action potential duration, Kv7.2/7.3 in neuronal excitability, Kv7.4 in hearing and an emerging role of Kv7.5 in vascular tone, increases the demand for channel modulating drugs that exhibit selectivity among Kv7 subtypes. Diclofenac, an anti-inflammatory drug, was found to be a novel Kv7.2/7.3 channel opener and was used as a template to synthesize new activators and inhibitors of neuronal KCNQ channels (Kv7.2/7.3 and Kv7.4). We compare affects of diclofenac on human Kv7.4 and Kv7.5 currents using A7r5 rat aortic smooth muscle cells as an expression system and perforated patch-clamp techniques. Diclofenac, at 100∈1/4M, increased maximal conductance of Kv7.4 channels by 1.5-fold and induced a negative shift in the activation curve (by 9mV). Surprisingly, the same concentration of diclofenac (100∈1/4M) reduced maximal conductance of Kv7.5 channels by 2-fold, but also induced a robust negative shift in the activation curve (by 30mV). For the both Kv7.4 and Kv7.5, application of diclofenac (100∈1/4M) reduced the deactivation rate of the current. For Kv7.4, the deactivation rate was 1.7-fold slower in the presence of diclofenac, independent of the voltage in the range from −120mV to −90mV. In contrast, for Kv7.5 the reduced deactivation rate in the presence of diclofenac was voltage-dependent, changing linearly from 2-fold at −120mV to 4-fold at −90mV. These differences in diclofenac action on two members of the Kv7 channel family may reflect structural differences between Kv7.4 and Kv7.5 and make diclofenac a useful tool to distinguish between Kv7.4 and Kv7.5 currents in native tissues.