Angiotensin II Modulates IKs by Multiple Mechanisms with Varying Outcomes

Abstract

Previous studies showed that acute angiotensin II (AngII) application decreases IKs in ventricular myocytes, but increases IKs in atrial myocytes from guinea-pig (GPV and GPA). Chronic AngII application (released by implanted mini-pump, 4 weeks) also decreases IKs in GPV but increases IKs in GPA. Extrapolating these observations to human heart suggests that AngII may increase the risk for long QT and atrial fibrillation by differentially remodeling ventricular and atrial IKs, respectively. Recently we identify a fundamental difference in IKs between GPV and GPA: KCNQ1 and KCNE1 (Q1 and E1, pore-forming and auxiliary IKs subunits) are largely separated in GPV (Q1 intracellular while E1 on surface) but better colocalized on cell surface in GPA. Furthermore, AngII incubation induces significant Q1 translocation to cell surface in GPV but not in GPA. We hypothesize that AngII modulation of IKs involves multiple signaling pathways, which develop with different time courses and exert differential effects on IKs. We test this hypothesis by coexpressing Q1, E1, and AngII-receptor (AT1R) in COS-7 cells, and monitor AngII (1 uM) effects on IKs using patch clamp recording, confocal imaging, and protein fractionation/biochemical quantification. Acute AngII exposure reduces IKs (some with early transient increase) and right shifts V0.5 of activation. Overexpressing Ca-binding-deficient calmodulin reduces these effects. Incubation with AngII for 1 or 24 hr followed by patch clamp in the absence of AngII shows that IKs is increased over time-control. Cell surface Q1 protein level is higher after 1-hr AngII incubation. After 24-hr AngII incubation, cell surface Q1 level is the same as time-control, but overall Q1 protein level is higher. These data suggest that AngII modulation of IKs involves [Ca]i elevation/PKC activation/PIP2 depletion (acute), Q1 translocation to cell surface (1 hr), changes in Q1 biosynthesis and/or degradation (24 hr).