Early Effects of High Intensity X-Radiation on Skeletal Muscle

Abstract

Following exposure of isolated frog gastrocnemii to high intensity x-radiation, increased fatigability and contracture of the muscles have been demonstrated in previous studies (3). The present paper presenting an expansion of these previous studies comprises, first, a study of cold blooded muscle during and after exposure to x-radiation and, second, a determination of radiation effects on muscles of intact warm blooded animals. RADIATION :EFFECTS ON COLD BLOODED MUSCLEThe first section of the present study was performed on isolated cold blooded gastrocnemii. This method offers an important advantage. Changes occurring in the muscle during and following irradiation, as compared to a non-irradiated control muscle, must be directly caused by the ionizing radiation, since all connections to other organs through the circulatory and nervous system are interrupted. MethodThe experiments were performed during the fall of the year with leopard frogs (Rana pipiens) of approximately equal size. The animals were stored at 6°C. Preparation, radiation, and testing of the isolated gastrocnemii were carried out at 20°C.Recordings of the isotonic contractions were made according to a method previously described (5). As an essential feature of this method alteration of muscle length produced proportional voltage changes at the slider of a micropotentiometer. These voltage changes were recorded either by means of a cathode ray oscilloscope or an ink writer.The plastic wet chamber containing the isolated gastrocnemius was placed in the head of a Picker x-ray unit. The conditions of the experiment were as follows: voltage, 260 kvp.; amperage; 18 ma.; inherent filtration, 0.25 ram. copper; additional filtration, 3 ram. plastic wall of wet chamber; and target-muscle distance, 8 cm. Under these conditions a dose rate of approximately 6 kr (6,000 r) per minute was measured in air.The experimentation was carried out in several distinct steps. Radiation effects were studied (1) on the work capacity, (2) on the single twitch, (3) on the lengthforce diagram, and (4) on the histology of the muscle. 445

Radiation damage in muscle cell membranes and regulation of cell metabolism

“…Mechanical parametersThe general results of these experiments agree with those of Gerstner, et al(2).Maximal contraction amplitude under load, as indicated by analysis of the length-force diagrams, decreases significantly in irradiated muscles. The latent periods and rise times of single twitches are not significantly different in control and irradiated muscles.…”

“…Length-force diagrams in the contracted state, latency and shape of single maximal twitches, and time to develop contracture in response to prolonged stimulation were studied following the procedures of Gerstner, et al (2) and Portela, et al (1). For "4 st.le tfltehos, 30 oeatiol ad 30 1zws4Laod ouao"AuS Omso were stimulated to lift a load of 32 gm by reotangular pulses of In any case, 190,00r increases the rate of potassium loss from frog sartorius muscles in K-free Ringer's solution by approximately 50%.…”

Behavioral effects of ionizing radiations.

“…With doses below 6,000 r. no abnormality may be observed (43). Gerstner, et al (21) applied 50,000 r. to the rabbit gastrocnemius and they noted that fatigue effects could be observed only when high performance was demanded by using a heavy load or a high frequency of stimulation.…”

Heavy Ion Microbeam Irradiation Induces Ultrastructural Changes in Isolated Single Fibers of Skeletal Muscle

“…It is also important to evaluate the effects of cosmic ray exposure in space activity, especially during extravehicular activity (Ohnishi and Ohnishi, 2004). However, in contrast to the large number of reports regarding alterations of physiological function (early fatigue, contracture, prolongation of relaxation time, and decreased contraction amplitude for heavy loads), histological changes, such as hyalinization and break-up of muscle fibers (Gerstner et al, 1954), myofibrillolysis and necrosis (Khan, 1974), edema (Nömayr et al, 2001), and release of amino acids, especially alanine and glutamine (Schwenen et al, 1989;Holecek et al, 2002) associated with exposure to X-or γ-rays, there have been no *To whom correspondence should be addressed: Hiroshi Yorifuji, Department of Neuromuscular and Developmental Anatomy, Division of Bioregulatory Medicine, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan.…”