Calcium Signaling and Contractility in Cardiac Myocyte of Wolframin Deficient Rats

Michal Cagalinec; Alexandra Zahradníková; Alexandra Zahradníková Jr; Dominika Kováčová; Ludovit Paulis; Simona Kureková; Matej Hot'ka; Jana Pavelková; Mario Plaas; Marta Novotová; Ivan Zahradník

doi:10.3389/fphys.2019.00172

Calcium Signaling and Contractility in Cardiac Myocyte of Wolframin Deficient Rats

Front Physiol. 2019 Mar 13:10:172. doi: 10.3389/fphys.2019.00172. eCollection 2019.

Authors

Michal Cagalinec^{1

2

3}, Alexandra Zahradníková^{1

2}, Alexandra Zahradníková Jr^{1

2}, Dominika Kováčová⁴, Ludovit Paulis^{4

5}, Simona Kureková², Matej Hot'ka^{2

6}, Jana Pavelková^{1

2}, Mario Plaas³, Marta Novotová^{1

2}, Ivan Zahradník^{1

2}

Affiliations

¹ Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, University Science Park for Biomedicine, Slovak Academy of Sciences, Bratislava, Slovakia.
² Institute of Molecular Physiology and Genetics, Centre of Biosciences, Slovak Academy of Sciences, Bratislava, Slovakia.
³ Institute of Biomedicine and Translational Medicine, Faculty of Medicine, University of Tartu, Tartu, Estonia.
⁴ Institute of Pathophysiology, Faculty of Medicine, Comenius University, Bratislava, Slovakia.
⁵ Institute of Normal and Pathological Physiology, Centre of Experimental Medicine, Slovak Academy of Sciences, Bratislava, Slovakia.
⁶ Department of Neurophysiology and Neuropharmacology, Center of Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.

Abstract

Wolframin (Wfs1) is a membrane protein of the sarco/endoplasmic reticulum. Wfs1 mutations are responsible for the Wolfram syndrome, characterized by diabetic and neurological symptoms. Although Wfs1 is expressed in cardiac muscle, its role in this tissue is not clear. We have characterized the effect of invalidation of Wfs1 on calcium signaling-related processes in isolated ventricular myocytes of exon5-Wfs1 deficient rats (Wfs1^-e5/-e5) before the onset of overt disease. Calcium transients and contraction were measured in field-stimulated isolated myocytes using confocal microscopy with calcium indicator fluo-3 AM and sarcomere length detection. Calcium currents and their calcium release-dependent inactivation were characterized in whole-cell patch-clamp experiments. At 4 months, Wfs1^-e5/-e5 animals were euglycemic, and echocardiographic examination revealed fully compensated cardiac function. In field-stimulated isolated ventricular myocytes, both the amplitude and the duration of contraction of Wfs1^-e5/-e5 animals were elevated relative to control Wfs1^+/+ littermates. Increased contractility of myocytes resulted largely from prolonged cytosolic calcium transients. Neither the amplitude of calcium currents nor their voltage dependence of activation differed between the two groups. Calcium currents in Wfs1^-e5/-e5 myocytes showed a larger extent of inactivation by short voltage prepulses applied to selectively induce calcium release-dependent inactivation of calcium current. Neither the calcium content of the sarcoplasmic reticulum, measured by application of 20 mmol/l caffeine, nor the expression of SERCA2, determined from Western blots, differed significantly in myocytes of Wfs1^-e5/-e5 animals compared to control ones. These experiments point to increased duration of calcium release in ventricular myocytes of Wfs1^-e5/-e5 animals. We speculate that the lack of functional wolframin might cause changes leading to upregulation of RyR2 channels resulting in prolongation of channel openings and/or a delay in termination of calcium release.

Keywords: Wolfram syndrome; calcium current; calcium transient; cardiac myocyte; contractility; wolframin.