Chronic SR Ca2+-ATPase Inhibition Causes Adaptive Changes in Cellular Ca2+ Transport

• Published in: Circulation research 2003-04, Vol.92 (7), p.769-776
• Main Authors: Brittsan, Angela G, Ginsburg, Kenneth S, Chu, Guoxiang, Yatani, Atsuko, Wolska, Beata M, Schmidt, Albrecht G, Asahi, Michio, MacLennan, David H, Bers, Donald M, Kranias, Evangelia G
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological - drug effects; Animals; Biological and medical sciences; Biological Transport - drug effects; Blotting, Western; Calcium - metabolism; Calcium Channels - physiology; Calcium-Binding Proteins - genetics; Calcium-Binding Proteins - metabolism; Calcium-Transporting ATPases - genetics; Calcium-Transporting ATPases - metabolism; Cell Line; Echocardiography; Female; Fundamental and applied biological sciences. Psychology; Heart; Heart Ventricles - cytology; Heart Ventricles - drug effects; Humans; Isoproterenol - pharmacology; Male; Membrane Potentials - drug effects; Mice; Mice, Inbred Strains; Mice, Knockout; Mice, Transgenic; Microsomes - metabolism; Mutation; Myocytes, Cardiac - cytology; Myocytes, Cardiac - drug effects; Myocytes, Cardiac - physiology; Patch-Clamp Techniques; Phosphorylation - drug effects; Rabbits; Sarcoplasmic Reticulum - metabolism; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Space life sciences; Transfection; Ventricular Function; Vertebrates: cardiovascular system
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.0000066661.49920.59

—Phospholamban, the critical regulator of the cardiac SERCA2a Ca affinity, is phosphorylated at Ser16 and Thr17 during β-adrenergic stimulation (eg, isoproterenol). To assess the impact of nonphosphorylatable phospholamban, a S16A, T17A double-mutant (DM) was introduced into phospholamban knockout mouse hearts. Transgenic lines expressing DM phospholamban at levels similar to wild types (WT) were identified. In vitro phosphorylation confirmed that DM phospholamban could not be phosphorylated, but produced the same shift in EC50 of SERCA2a for Ca as unphosphorylated WT phospholamban. Rates of basal twitch [Ca]i decline were not different in DM versus WT cardiomyocytes. Isoproterenol increased the rates of twitch [Ca]i decline in WT, but not DM myocytes, confirming the prominent role of phospholamban phosphorylation in this response. Increased L-type Ca current (ICa) density, with unaltered characteristics, was the major compensation in DM myocytes. Consequently, the normal β-adrenergic-induced increase in ICa caused larger dynamic changes in absolute ICa density. Isoproterenol increased Ca transients to a comparable amplitude in DM and WT. There were no changes in myofilament Ca sensitivity, or the expression levels and Ca removal activities of other Ca-handling proteins. Nor was there evidence of cardiac remodeling up to 10 months of age. Thus, chronic inhibition of SERCA2a by ablation of phospholamban phosphorylation (abolishing its adrenergic regulation) results in a unique cellular adaptation involving greater dynamic ICa modulation. This ICa modulation may partly compensate for the loss in SERCA2a responsiveness and thereby partially normalize β-adrenergic inotropy in DM phospholamban mice. (Circ Res. 2003;92:769–776.)