Increased calcium leak associated with reduced calsequestrin expression in hyperthyroid cardiomyocytes.
Calcium (Ca2+) leak during cardiac diastole is chiefly mediated by intracellular Ca2+channel/Ryanodine Receptors. Increased diastolic Ca2+leak has been proposed as the mechanism underlying the appearance of hereditary arrhythmias. However, little is known about alterations in diastolic Ca2+leak and the specific roles played by key intracellular Ca2+-handling proteins in hyperthyroidism, a known arrhythmogenic condition.



We sought to determine whether there were modifications in diastolic Ca2+leak, based on the recording of Ca2+sparks and Ca2+waves; we also investigated changes in the expression and activity of key Ca2+handling proteins, including ryanodine receptors, Sarco-Endoplasmic Reticulum Ca2+ATPase pump and calsequestrin in isolated left-ventricular cardiomyocytes isolated from hyperthyroid rats.



Electrocardiography (ECG) recordings were performed in control and hyperthyroid rats. Ca2+sparks, Ca2+waves, and electrically-stimulated Ca2+transients were recorded in Fluo-3-loaded cardiomyocytes from both experimental groups using confocal microscopy. In addition, left-ventricular homogenates and Ryanodine Receptor-enriched membrane fractions were prepared for assessing [3H]-ryanodine binding, hydrolytic ATPase activity of SERCA pump and expression levels of key proteins by Western blot, and cDNA for real-time qPCR.



Extrasystoles were observed in hearts of hyperthyroid rats by ECG recordings. Arrhythmogenic activity, high incidence of Ca2+waves, and de novo Ca2+wavelets -in the absence of sarcoplasmic reticulum Ca2+overload- were recorded in these cardiomyocytes. The exacerbated diastolic Ca2+leak and arrhythmogenic activities were related to a diminished expression of calsequestrin along with increased SERCA pump activity, which, in effect, promoted a gain-of-function in RyRs without alterations in SR Ca2+load, RyR expression or its Ca2+sensitivity.
Department of Biochemistry, Cinvestav-IPN, Mexico City, Mexico.
David R
DR
de Alba-Aguayo
Department of Pharmacology, Instituto Nacional de Cardiología "Ignacio Chávez", Mexico City, Mexico.
Natalia
N
Pavón
Department of Biochemistry, Cinvestav-IPN, Mexico City, Mexico.
Martha
M
Mercado-Morales
Department of Biochemistry, Cinvestav-IPN, Mexico City, Mexico.
Miyamin
M
Miranda-Saturnino
Posgrado en Ciencias Genómicas, Universidad Autónoma de la Ciudad de Mexico, Mexico City, Mexico.
Mavil
M
López-Casamichana
Department of Biochemistry, Cinvestav-IPN, Mexico City, Mexico.
Agustin
A
Guerrero-Hernández
Department of Biochemistry, Cinvestav-IPN, Mexico City, Mexico; Center for Arrhythmia Research, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, 48109, USA. Electronic address: arueda@cinvestav.mx.
Angelica
A
Rueda
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D002155:Calsequestrin; D006980:Hyperthyroidism / Q000378:metabolism*; D008297:Male; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
D002135:Calcium-Binding Proteins; D002155:Calsequestrin; C057137:Casq1 protein, rat; D002118:Calcium
Calsequestrin; Cardiac arrhythmia; Diastolic calcium leak; Hyperthyroidism; Ryanodine receptor; SERCA pump