Casq2 deletion causes sarcoplasmic reticulum volume increase, premature Ca2+ release, and catecholaminergic polymorphic ventricular tachycardia
Björn C. Knollmann, … , Clara Franzini-Armstrong, Karl Pfeifer
Björn C. Knollmann, … , Clara Franzini-Armstrong, Karl Pfeifer
Published September 1, 2006
Citation Information: J Clin Invest. 2006;116(9):2510-2520. https://doi.org/10.1172/JCI29128.
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Research Article Cardiology

Casq2 deletion causes sarcoplasmic reticulum volume increase, premature Ca2+ release, and catecholaminergic polymorphic ventricular tachycardia

Abstract

Cardiac calsequestrin (Casq2) is thought to be the key sarcoplasmic reticulum (SR) Ca2+ storage protein essential for SR Ca2+ release in mammalian heart. Human CASQ2 mutations are associated with catecholaminergic ventricular tachycardia. However, homozygous mutation carriers presumably lacking functional Casq2 display surprisingly normal cardiac contractility. Here we show that Casq2-null mice are viable and display normal SR Ca2+ release and contractile function under basal conditions. The mice exhibited striking increases in SR volume and near absence of the Casq2-binding proteins triadin-1 and junctin; upregulation of other Ca2+-binding proteins was not apparent. Exposure to catecholamines in Casq2-null myocytes caused increased diastolic SR Ca2+ leak, resulting in premature spontaneous SR Ca2+ releases and triggered beats. In vivo, Casq2-null mice phenocopied the human arrhythmias. Thus, while the unique molecular and anatomic adaptive response to Casq2 deletion maintains functional SR Ca2+ storage, lack of Casq2 also causes increased diastolic SR Ca2+ leak, rendering Casq2-null mice susceptible to catecholaminergic ventricular arrhythmias.

Authors

Björn C. Knollmann, Nagesh Chopra, Thinn Hlaing, Brandy Akin, Tao Yang, Kristen Ettensohn, Barbara E.C. Knollmann, Kenneth D. Horton, Neil J. Weissman, Izabela Holinstat, Wei Zhang, Dan M. Roden, Larry R. Jones, Clara Franzini-Armstrong, Karl Pfeifer

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Figure 5

Casq2–/– myocytes have largely preserved SR Ca2+ release and SR Ca2+ content under basal conditions, but isoproterenol application causes increased SR Ca2+ leak.

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Casq2–/– myocytes have largely preserved SR Ca2+ release and SR Ca2+ co...
(A) Representative examples of rapid application of caffeine (10 mmol/l) to a Casq2+/+ (top) and a Casq2–/– myocyte (bottom). Myocytes were field stimulated at 1 Hz to maintain consistent SR Ca2+ load. Note the increased twitch transient and caffeine-induced transients in the presence of ISO (1 μmol/l; right). The height of the caffeine-induced Ca2+ transient was used as a measure of total SR Ca2+ content (30). Fractional SR Ca2+ release was calculated by dividing the height of the last twitch transient by the height of the caffeine transient. (B) Comparison of average SR Ca2+ content (left) and fractional SR Ca2+ release (right). *P < 0.05, **P < 0.01. Casq2+/+ myocytes: n = 41 (baseline) and 27 (ISO); Casq2–/–myocytes: n = 70 (baseline) and 37 (ISO). (C) Protocol used to measure SR Ca2+ leak as described in ref. 32. Plasma membrane Ca2+ flux is eliminated by removal of extracellular Na+ and Ca2+. The drop in steady-state [Ca2+]i (double arrow) represents a shift of Ca2+ from the cytosol to the SR when RyR2 channels are inhibited by tetracaine (1 mmol/l) and was used as a measure of SR Ca2+ leak. (D) Comparison of average SR Ca2+ leak (left) and SR Ca2+ content in the presence of tetracaine (right). Note that when SR Ca2+ leak was blocked by tetracaine, SR Ca2+ content was not significantly different between the 2 groups. **P < 0.01. Casq2+/+ myocytes: n = 32 (baseline) and 45 (ISO); Casq2–/–myocytes: n = 29 (baseline) and 42 (ISO). (E) SR Ca2+ leak in the presence of ISO plotted as a function of SR Ca2+ content. Note that the SR Ca2+ leak of Casq2–/– myocytes remained SR load dependent but was shifted to the left compared with that of Casq2+/+ myocytes.