An Electron Microscope Study of Calcium and Magnesium in Smooth Muscle.

Abstract

Recent investigations of electrolytes in Thyone muscle by Steinbach have led him to the conclusion that Ca is present in cells in lower concentration than that of the surrounding medium. Since these results are at variance with our own in a number of respects we have studied again the localization of Ca and Mg in mammalian and frog smooth muscle by the electron microscope as described by Scott and Packer. Naturally, the results obtained cannot be compared directly with those of Steinbach as the same form was not used. Furthermore, our interest lay in determining the localization in smooth muscle cells which had been preserved as nearly as possible in their normal physiological state. Thin strips of smooth muscle were taken from the duodenum and stomach wall of cats and frogs. These pieces were frozen in liquid air while still actively contracting from the mechanical stimulation of the manipulation. The frozen tissues were dehydrated in vacuo at -63°C and infiltrated in water-free paraffin without breaking the vacuum. This procedure precludes any salt shift during dehydration and the addition of water from outside sources at any time and thus maintains the spatial relations of the element in question. Thin sections (8μ) of muscle were prepared and examined by heating on a surfaced cathode in the electron microscope. The technic of preparation of tissues for examination and the method of localizing Ca and Mg are believed to preserve the exact topical cellular relationships. Unfortunately, it is impossible by the method used to differentiate Ca and Mg, since both activate the cathode surface. Quantities of these elements in less than 1 × 10-12 g are easily detected. In no instance was either Ca or Mg found outside the cell wall.