Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA032

Poster Communications

A phospholipase A2 homologue increases the intracellular calcium concentration and induces spontaneous intracellular calcium transients and cell collapse in adult rat cardiomyocytes

A. J. Lopez-Davila1, N. Weber1, T. Kraft1, M. Arias-Hidalgo2,3, J. Fernández4, J. Gutiérrez4, B. Lomonte4

1. Institute for Molecular and Cell Physiology, Hannover Medical School, Hannover, Germany. 2. Institute for Molecular and Cell Physiology, AG Vegetative Physiologie, Hannover Medical School, Hannover, Germany. 3. Departamento de Fisiología, Universidad de Costa Rica, San José, Costa Rica. 4. Instituto Clodomiro Picado, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica.

The group of phospholipase A2 and phospholipase A2 homologue muscle toxins (PLA2-Myotoxins) from the venom of the viperid snake Bothrops asper targets skeletal muscle cells. Muscular effects of PLA2-Myotoxins include triggering spontaneous intracellular calcium transients, cell membrane disruption, hypercontraction of the myofilaments and cell collapse. Through those and other effects PLA2-Myotoxins lead to irreversible skeletal muscle damage. Whether and how PLA2-Myotoxins additionally target cardiac muscle cells has remained unknown. In order to test for the first time the effects of PLA2-myotoxins in the excitation-contraction coupling of adult cardiac muscle cells, we exposed vital rat cardiomyocytes to the PLA2 homologue myotoxin II (PLA2-MtII). Anesthesia of rats was induced by inhalation of 5% isoflurane for 3 min in a box and kept by continuous inhalation of 2% isoflurane through a mask. After confirming the anesthetized state by the absence of reaction to several nociceptive stimuli, the heart was rapidly excised and a primary culture of vital ventricular cardiomyocytes was isolated. Thereafter, single cardiomyocytes were exposed to 50 µg/mL PLA2-MtII while monitoring intracellular calcium concentration (as reported by the calcium indicator FURA-2) and isotonic unloaded cell shortening by means of changes of the sarcomere length, during cyclic electrical stimulation (1 Hz). Electrical stimulation triggered calcium transients and cell shortening in cardiac cells. Compared with the baseline before toxin application, few seconds of exposition to PLA2-MtII induced in the cardiomyocytes: a) increased diastolic and systolic calcium concentration, b) increased amplitude of the calcium transient, c) increased rate constant of calcium concentration decay during the descending phase of the calcium transient and d) increased amplitude of cell shortening. These changes reached statistical significance levels (p< 0.05, T-test). Additionally, if kept in presence of PLA2-MtII for few minutes, cardiomyocytes progressively lost the calcium transient and cell shortening triggered by the electrical stimulus, showed spontaneous intracellular calcium transients and finally collapsed. Cell collapse was characterized by membrane damage, irreversible hypercontraction and abnormally increased intracellular calcium concentration. Thus, our results suggest that PLA2-MtII induces alterations of the intracellular calcium handling and structural damage in adult cardiac muscle cells in vitro. Understanding the membrane and intracellular mechanisms triggered by PLA2-Myotoxins in cardiac muscle could contribute to understand snakebite envenoming as well as to develop new molecular tools for manipulating the intracellular calcium concentration of the heart.

Where applicable, experiments conform with Society ethical requirements