Effects of hypertrophic challenge on small-conductance, Ca2+-activated K+(SK2) channel expression were explored in intact murine hearts, isolated ventricular myocytes and neonatal rat cardiomyocytes (NRCMs). An established experimental platform applied
angiotensin II (Ang II) challenge in the presence and absence of reduced
p21-activated kinase (PAK1) (PAK1cko vs. PAK1f/f, or
shRNA-PAK1 interference) expression. SK2 current contributions were detected through their sensitivity to
apamin block. Ang II treatment increased such SK2 contributions to optically mapped action potential durations (APD80) and their heterogeneity, and to patch-clamp currents. Such changes were accentuated in PAK1cko compared to PAK1f/f, intact hearts and isolated cardiomyocytes. They paralleled increased histological and echocardiographic hypertrophic indices, reduced cardiac contractility, and increased SK2
protein expression, changes similarly greater with PAK1cko than PAK1f/f. In NRCMs, Ang II challenge replicated such increases in
apamin-sensitive SK patch clamp currents as well as in real-time PCR and western blot measures of SK2
mRNA and
protein expression and cell
hypertrophy. Furthermore, the latter were enhanced by shRNA-PAK1 interference and mitigated by the PAK1 agonist
FTY720. Increased
CaMKII and CREB phosphorylation accompanied these effects. These were rescued by both
FTY720 as well as the
CaMKII inhibitor
KN93, but not its inactive analogue KN92. Such CREB then specifically bound to the KCNN2 promoter sequence in
luciferase assays. These findings associate Ang II induced
hypertrophy with increased SK2 expression brought about by a
CaMKII/CREB signaling convergent with the PAK1 pathway thence upregulating the KCNN2 promoter activity. SK2 may then influence cardiac electrophysiology under conditions of
cardiac hypertrophy and failure.