Book of Abstracts - New Frontiers 2022

Abstracts of oral presentations

IMPAIRMENT OF CALCIUM DYNAMICS AND CONTRACTILITY IN CARDIOMYOCYTES OF WOLFRAMIN INVALIDATED RATS

M. Cagalinec , A. Zahradníková Jr., J. Pavelková, M. Novotová, A. Zahradníková

Dept. of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center, Slovak Academy of Sciences, Bratislava, Slovakia

Wolfram syndrome (WS) is a rare recessive disorder caused by mutations in the Wfs1 gene encoding the wolframin protein (Wfs1). Wfs1 is located in the membrane of the endoplasmic reticulum (ER) and is involved in ER stress, mitochondrial function, and calcium signalling [1]. Since calcium is the principal trigger of cardiomyocyte contraction and since Wfs1 is highly expressed in the cardiac tissue [2], we have evaluated calcium metabolism and contractility in the Wfs1 exon5-deleted (Wfs1-e5/-e5) cardiac myocytes using confocal microscopy, patch-clamp, transmission molecular biology and electron microscopy [3]. In four months old male rats, invalidation of Wfs1 resulted in a significant increase of the amplitude of myocyte contraction as well as in prolongation of contraction in field-stimulated myocytes. The Fluo-3/AM stained Wfs1-e5/-e5 myocytes, recorded simultaneously with contractions, showed significantly prolonged calcium transient, but no significant change in the amplitude. Moreover, sarcoplasmic reticulum calcium content was not changed in the absence of functional Wfs1, as revealed by caffeine application. The change in contractility could result from a change in the calcium current (ICa, the trigger for calcium release) and/or from a change in calcium release itself. Calcium currents showed no statistically significant difference in voltage-dependent activation, inactivation, or peak amplitude. On the other hand, the extent of calcium release-dependent inactivation of ICa was significantly higher in Wfs1 e5/-e5 myocytes. Expression of the plasma membrane sodium-calcium exchanger (NCX) in Wfs1-e5/-e5 myocytes was decreased both at the mRNA and the protein level, whereas the expression levels of L-type calcium channel, RyR2, SERCA2, and CSQ2 were unchanged [4]. The decreased NCX expression might slow down Ca 2+ extrusion from myocytes, prolong calcium transients, and curtail ICa due to increased calcium release dependent inactivation. This would explain the unchanged SR calcium content. Finally, electron microscopic examination of the cardiac myocyte ultrastructure revealed variability in diameter of t-tubule profiles in dyads and higher occurrence of small non-dyadic t-tubules near Z-lines in the Wfs1 e5/ e5 group. In conclusion, the Wfs1 invalidation negatively impacts calcium handling and contractility of cardiac myocytes before the onset of diabetes at the organism level. References [1] M. Cagalinec, et al., PLoS Biol (2016), 14(7), e1002511. [2] T. Yamada, et al., Hum Mol Genet (2006), 15(10), 1600-1609. [3] M. Cagalinec, et al., Front Physiol (2019) Mar 13;10:172. [4] S. Kureková, M. Plaas, M. Cagalinec, Gen Physiol Biophys (2020), Sep;39(5):499 -503.

Keywords: Wolfram syndrome, cardiac myocyte, calcium signalling, contractility, patch clamp, ultrastructure

Funding: APVV-15-0302, VEGA 2/0121/19, VEGA 2/0143/17 and ITMS 26230120006.

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