Angiotensin II upregulates KCa3.1 channels and stimulates cell proliferation in rat cardiac fibroblasts

Abstract

The proliferation of cardiac fibroblasts is implicated in the pathogenesis of myocardial remodeling and fibrosis. Intermediate-conductance calcium-activated K+ channels (KCa3.1 channels) have important roles in cell proliferation. However, it is unknown whether angiotensin II (Ang II), a potent profibrotic molecule, would regulate KCa3.1 channels in cardiac fibroblasts and participate in cell proliferation. In the present study, we investigated whether KCa3.1 channels were regulated by Ang II, and how the channel activity mediated cell proliferation in cultured adult rat cardiac fibroblasts using electrophysiology and biochemical approaches. It was found that mRNA, protein, and current density of KCa3.1 channels were greatly enhanced in cultured cardiac fibroblasts treated with 1 μM Ang II, and the effects were countered by the angiotensin type 1 receptor (AT1R) blocker losartan, the p38-MAPK inhibitor SB203580, the ERK1/2 inhibitor PD98059, and the PI3K/Akt inhibitor LY294002. Ang II stimulated cell proliferation and the effect was antagonized by the KCa3.1 blocker TRAM-34 and siRNA targeting KCa3.1. In addition, Ang II-induced increase of KCa3.1 expression was attenuated by transfection of activator protein-1 (AP-1) decoy oligodeoxynucleotides. These results demonstrate for the first time that Ang II stimulates cell proliferation mediated by upregulating KCa3.1 channels via interacting with the AT1R and activating AP-1 complex through ERK1/2, p38-MAPK and PI3K/Akt signaling pathways in cultured adult rat cardiac fibroblasts.