γ-Radiation induces apoptosis via sarcoplasmatic reticulum in guinea pig ileum smooth muscle cells

• Published in: European journal of pharmacology Vol. 590; no. 1; pp. 20 - 28
• Main Authors: Claro, Sandra, Oshiro, Maria Etsuko Miyamoto, Freymuller, Edna, Katchburian, Eduardo, Kallas, Esper George, Cerri, Paulo Sérgio, Ferreira, Alice Teixeira
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 20.08.2008; Elsevier
• Subjects: Animals; Apoptosis; Apoptosis - radiation effects; Biological and medical sciences; Calcium; Calcium - metabolism; Caspase 12; Caspases - physiology; Cells, Cultured; Egtazic Acid - analogs & derivatives; Egtazic Acid - pharmacology; Gamma Rays; Guinea Pigs; Ileum; Ileum - physiology; Ileum - radiation effects; Medical sciences; Muscle Contraction - radiation effects; Myocytes, Smooth Muscle - physiology; Myocytes, Smooth Muscle - radiation effects; Pharmacology. Drug treatments; Sarco/endoplasmic reticulum; Sarcoplasmic Reticulum - physiology; Sarcoplasmic Reticulum - radiation effects; γ-Radiation; Caspase 12; Calcium; Ileum; Sarco/endoplasmic reticulum; γ-Radiation; Apoptosis; Digestive system; Enzyme; Cysteine endopeptidases; Rodentia; Caspase; Smooth muscle; Inorganic element; Small intestine; In vitro; Peptidases; Vertebrata; Mammalia; Guinea pig; Cell death; Animal; Hydrolases; Endoplasmic reticulum
• ISSN: 0014-2999; 1879-0712
• DOI: 10.1016/j.ejphar.2008.05.038

We investigated the effects of γ-radiation on cells isolated from the longitudinal smooth muscle layer of the guinea pig ileum, a relatively radioresistant tissue. Single doses (up to 50 Gy) reduced the amount of sarcoplasmatic reticulum and condensed the myofibrils, as shown by electron microscopy 3 days post-irradiation. After that, contractility of smooth muscle strips was reduced. Ca 2+ handling was altered after irradiation, as shown in fura-2 loaded cells, with elevated basal intracellular Ca 2+, reduced amount of intrareticular Ca 2+, and reduced capacitive Ca 2+ entry. Radiation also induced apoptosis, judged from flow cytometry of cells loaded with proprium iodide. Electron microscopy showed that radiation caused condensation of chromatin in dense masses around the nuclear envelope, the presence of apoptotic bodies, fragmentation of the nucleus, detachment of cells from their neighbors, and reductions in cell volume. Radiation also caused activation of caspase 12. Apoptosis was reduced by the administration of the caspase inhibitor Z-Val-Ala-Asp-fluoromethyl-ketone methyl ester (Z-VAD-FMK) during the 3 day period after irradiation, and by the chelator of intracellular Ca 2+, 1,2-bis( o-aminophenoxy)-ethane- N,N,N′ ,N′-tetraacetic acid (BAPTA), from 1 h before until 2 h after irradiation. BAPTA also reduced the effects of radiation on contractility, basal intracellular Ca 2+, amount of intrareticular Ca 2+, capacitative Ca 2+ entry, and apoptosis. In conclusion, the effects of gamma radiation on contractility, Ca 2+ handling, and apoptosis appear due to a toxic action of intracellular Ca 2+. Ca 2+-induced damage to the sarcoplasmatic reticulum seems a key event in impaired Ca 2+ handling and apoptosis induced by γ-radiation.