Localization of Ca in muscles hindered in contraction by D2O.

Electron microscopic autoradiographic investigations have been made to study the localization of Ca in the muscle the contraction of which was broken by soak in 99.8 per cent heavy water. The distribution of autoradiographic grains, originating from Ca-45 ingested by previous incubation, above longitudinal sections of these muscles were compared to the distribution of grains above muscles not treated in heavy water. Considerable difference in grain density was found above the A- and I-bands of the two different kinds of muscle and above their sarcoplasmic reticulum. The investigations concerning the sarcoplasmic reticulum were completed by the study of distribution of autoradiographic grains above the transversal sections of these muscles.