ATP-INDUCED CALCIUM INCREASE AS A POTENTIAL FIRST SIGNAL IN MECHANICAL TISSUE TRAUMA. A LASER SCANNING MICROSCOPIC STUDY ON CULTURED MOUSE SKELETAL MYOCYTES

Abstract

Although it is known that after major tissue trauma, local incidents in the mechanically destroyed muscle tissue form the basis of subsequently occurring severe inflammatory reactions, the very first events taking place immediately after myocyte destruction have not been studied on the single cell level thus far. Therefore, in this study, the reaction of cultured C2C12 mouse skeletal myocytes to lethal injury was examined using laser scanning microscopy. Mechanical rupture of one single myocyte induced an immediate accumulation of calcium in its cytosol and nuclei, as detected by an increase in the fluorescence intensity of the intracellular calcium-sensitive dye Fluo-3. The intracellular calcium elevation propagated further to the adjacent, noninjured myocytes in a wave-like fashion within seconds. The calcium increase detected in these neighboring cells was higher and up to 1000 times more extended than the physiological calcium spike that induces C2C12 myocyte contraction. Wave propagation did not depend on gap junctional communication but occurred via liberation of nucleotides, mainly ATP, but presumably also UTP and others, from the destroyed cell and subsequent calcium release from the sarcoplasmic reticulum via a purinoceptor-mediated mechanism in the adjacent cells. These findings suggest a decisive role of ATP and related nucleotides in the pathogenesis of tissue trauma because they appear to initiate the signaling mechanism from injured myocytes to the surrounding tissue and potentially to the whole body.