Polyunsaturated fatty acids produce a range of activators for heterogeneous IKs channel dysfunction

Abstract

Repolarization and termination of the ventricular cardiac action potential is highly dependent on the activation of the slow delayed-rectifier potassium IKs channel. Disruption of the IKs current leads to the most common form of congenital long QT syndrome (LQTS), a disease that predisposes patients to ventricular arrhythmias and sudden cardiac death. We previously demonstrated that polyunsaturated fatty acid (PUFA) analogues increase outward K+ current in wild type and LQTS-causing mutant IKs channels. Our group has also demonstrated the necessity of a negatively charged PUFA head group for potent activation of the IKs channel through electrostatic interactions with the voltage-sensing and pore domains. Here, we test whether the efficacy of the PUFAs can be tuned by the presence of different functional groups in the PUFA head, thereby altering the electrostatic interactions of the PUFA head group with the voltage sensor or the pore. We show that PUFA analogues with taurine and cysteic head groups produced the most potent activation of IKs channels, largely by shifting the voltage dependence of activation. In comparison, the effect on voltage dependence of PUFA analogues with glycine and aspartate head groups was half that of the taurine and cysteic head groups, whereas the effect on maximal conductance was similar. Increasing the number of potentially negatively charged moieties did not enhance the effects of the PUFA on the IKs channel. Our results show that one can tune the efficacy of PUFAs on IKs channels by altering the pKa of the PUFA head group. Different PUFAs with different efficacy on IKs channels could be developed into more personalized treatments for LQTS patients with a varying degree of IKs channel dysfunction.

Polyunsaturated Fatty Acids as Modulators of KV7 Channels

“…By comparison, 20 µM of EPA slowed activation kinetics for K V 7.1/KCNE1 without affecting current amplitude (Doolan et al, 2002). In contrast, we report that DHA at concentrations of 7 µM or higher shifts V 50 of K V 7.1 toward negative voltages and that the presence of KCNE1 largely abolishes this V 50 effect (Liin et al, 2015;Bohannon et al, 2020). However, we observe a DHAinduced increase in K V 7.1/KCNE1 current amplitude and G max (Bohannon et al, 2020).…”

“…Another aspect to consider may be the method of PUFA application. We note larger DHA effects on current amplitude upon constant DHA perfusion compared to a single DHA application (Liin et al, 2015;Bohannon et al, 2020). Both Doolan et al, and Moreno et al, describe results employing PUFA perfusion.…”

“…In contrast, we report that DHA at concentrations of 7 µM or higher shifts V 50 of K V 7.1 toward negative voltages and that the presence of KCNE1 largely abolishes this V 50 effect (Liin et al, 2015;Bohannon et al, 2020). However, we observe a DHAinduced increase in K V 7.1/KCNE1 current amplitude and G max (Bohannon et al, 2020). A third study, by Moreno and colleagues, reports that 20 µM of DHA or EPA increases K V 7.1/KCNE1 current amplitude and shifts V 50 of K V 7.1/KCNE1 toward negative voltages (Moreno et al, 2015).…”

“…as increase in G max in Table 1; Bohannon et al, 2020). Both the shift in V 50 and increase in G max may contribute to the overall increase in current amplitude at different voltages.…”

“…Polyunsaturated fatty acid analogs with lower head-group pKa values have been instrumental in determining the mechanism of action of PUFAs on K V 7.1. PUFA analogs with glycine or taurine head-groups have estimated pKa values that are 1 and 5.5 units lower than that of carboxyl head-groups, respectively, (Bohannon et al, 2020), and are examples of PUFA analogs with exaggerated acute effects on V 50 of both K V 7.1 and K V 7.1/KCNE1 at physiological pH (Liin et al, 2015). In experiments utilizing DHA-glycine (DHA-Gly) or AA-taurine (N-AT), we have shown that PUFA analogs interact with S4 to shift V 50 .…”