NADPH oxidase (NOX) derived superoxide (O2.‐) upregulates intermediate‐conductance Ca2+ ‐ activated K+ channel (KCa3.1) expression in vascular smooth muscle cells (VSMCs)

Abstract

Reactive oxygen species (ROS), predominantly from NOX, mediate VSMC phenotypic modulation known to play a role in hypertension, atherosclerosis, and hypertrophy. We have previously shown that upregulation of KCa3.1 via increased AP‐1 activity is required for phenotypic modulation of porcine coronary smooth muscle cells (PCSMC). However, the role of ROS in KCa3.1 regulation remains unknown. Our objective was to determine if NOX regulates KCa3.1 expression via AP‐1. Basic fibroblast growth factor (bFGF, 25ng/mL) increased O2.−production in PCSMC, while the NOX inhibitor apocynin (Apo, 1mM) completely abolished O2.− production. bFGF increased KCa3.1 mRNA levels 2.5 fold; while decreasing smooth muscle myosin heavy chain mRNA levels 80% (P< 0.05) in PCSMC. Apo completely inhibited KCa3.1 mRNA upregulation indicating that NOX derived O2.−is required for KCa3.1 upregulation. Acute bFGF significantly increased K+ current, which was inhibited ~50% by the KCa3.1 specific channel blocker TRAM‐34 (100nM) indicating that bFGF causes an upregulation in KCa3.1 channel activity. bFGF increased AP‐1 promoter activity 2.5 fold, while Apo completely inhibited the response to bFGF. These results support a novel mechanism by which NOX derived O2.− regulates KCa3.1 expression through AP‐1.