Acute phosphatidylinositol 4,5 bisphosphate depletion destabilizes sarcolemmal expression of cardiac L-type Ca 2+ channel Ca V 1.2.

Ca V 1.2 channels are critical players in cardiac excitation-contraction coupling, yet we do not understand how they are affected by an important therapeutic target of heart failure drugs and regulator of blood pressure, angiotensin II. Signaling through G q -coupled AT1 receptors, angiotensin II triggers a decrease in PIP 2 , a phosphoinositide component of the plasma membrane (PM) and known regulator of many ion channels. PIP 2 depletion suppresses Ca V 1.2 currents in heterologous expression systems but the mechanism of this regulation and whether a similar phenomenon occurs in cardiomyocytes is unknown. Previous studies have shown that Ca V 1.2 currents are also suppressed by angiotensin II. We hypothesized that these two observations are linked and that PIP 2 stabilizes Ca V 1.2 expression at the PM and angiotensin II depresses cardiac excitability by stimulating PIP 2 depletion and destabilization of Ca V 1.2 expression. We tested this hypothesis and report that Ca V 1.2 channels in tsA201 cells are destabilized after AT1 receptor-triggered PIP 2 depletion, leading to their dynamin-dependent endocytosis. Likewise, in cardiomyocytes, angiotensin II decreased t-tubular Ca V 1.2 expression and cluster size by inducing their dynamic removal from the sarcolemma. These effects were abrogated by PIP 2 supplementation. Functional data revealed acute angiotensin II reduced Ca V 1.2 currents and Ca 2+ transient amplitudes thus diminishing excitation-contraction coupling. Finally, mass spectrometry results indicated whole-heart levels of PIP 2 are decreased by acute angiotensin II treatment. Based on these observations, we propose a model wherein PIP 2 stabilizes Ca V 1.2 membrane lifetimes, and angiotensin II-induced PIP 2 depletion destabilizes sarcolemmal Ca V 1.2, triggering their removal, and the acute reduction of Ca V 1.2 currents and contractility.