Book of Abstracts - New Frontiers 2022

Abstracts of poster presentations

FORMATION OF DYADS DURING POSTNATAL CARDIAC DEVELOPMENT IN RATS

A. Zahradnikova Jr. 1 , S. Kezmarova 2 , M. Novotova 1 , I. Zahradnik 1 , A. Zahradnikova 1

1 Department of Cellular Cardiology, Institute of Experimental Endocrinology, Biomedical Research Center of the Slovak Academy of Sciences, Bratislava, Slovakia; 2 Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia A fast increase of cytosolic Ca 2+ concentration is necessary for the efficient contraction of cardiac myocytes. In adult mammals, this is achieved mostly by calcium-induced calcium release from the intracellular Ca 2+ store (sarcoplasmic reticulum; SR) at specialized subcellular structures – dyads. Here, the sarcolemmal tubules come into contact with terminal cisternae of the SR containing ryanodine receptor calcium release channels (RyR2). The whole structure is held together, and the distance between the outer and inner membrane is maintained by the structural protein Junctophilin-2 (JP2). In newborn mammals, however, cardiac myocytes are not fully differentiated and still depend on Ca 2+ influx from the extracellular space for their contraction. Transformation of excitation-contraction coupling (ECC) from the neonatal to the adult form involves structural and functional changes that are not well understood yet. We studied the localization of the key proteins of cardiac excitation-contraction coupling - the sarcolemmal voltage-dependent calcium channels (Cav1.2) and the RyR2 and JP2 of SR in cardiomyocytes of developing rats on days 3 to 20 post-partum and of adult rat hearts. We have used confocal microscopy with multiplex immunofluorescent labelling and fluorescently conjugated wheat-germ agglutinin membrane probe, and transmission electron microscopy to identify the co-localization of specific antibodies and the development of dyads. Localization of RyR2 channels followed sarcomeric distribution from the early days on. In contrast, Cav1.2 and JP2 were first localized predominantly at the surface sarcolemma, but later predominantly at the newly formed tubular sarcolemma, appearing in parallel to the growth of myocyte volume. This process was accompanied by an increased extent of co-localization of the three proteins, which occurred almost solely at the cell surface up to 7-8 days post-partum, but translocated to the cell interior during maturation. Fully developed dyads were observed by electron microscopy on day 4 only at the lateral sarcolemma, while on day 9 they were observed at both the lateral and tubular sarcolemma. These findings indicate concerted development of dyads together with co-localization of their key proteins and proliferation of the sarcolemmal tubular system during the post-natal differentiation and growth of cardiomyocytes.

Keywords: EC coupling, dyads, cardiomyocytes

Funding: VEGA 2/0182/21, VEGA-2/0091/19, VEGA-2/0143/17, APVV-15-0302, and ITMS 26230120006

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