A histochemical study of cadmium binding with frog cardiac muscle fiber

Abstract

Chemical analysis on the cadmium content in various organs disclosed that trace of cadmium was found even in the hearts of some healthy animals and men1,2) . As a large amount of cadmium was found in the heart of patient of chronic cadmium intoxication3) cadmium is considered to have high affinity to some structural components of the hearts . On the other hand, it has been suggested from the authors' electrophysiological experiments on the contractility of the frog heart that Cd ions may competitively occupy the marginal zone of the cardiac muscle fiber where Ca ions normally exist" . The purpose of the present paper is to demonstrate histochemically the binding of Cd with the frog cardiac muscle fiber.The hearts of bull frogs (Rana catesbeiana) were excised out immediately after intrathecal urethane anethesia (1g per kg body weight) . The hearts were divided into two or four strips along the heart axes . One halves of the hearts were soaked into Ringer's solution (NaCl 110 mM, KC1 2 mM, CaC12 1 mM, glucose 10 mM, tris buffer 10 mM, pH 7.2) containing various concentrations of Cd and the other halves of the hearts were soaked into Ringer's solution without Cd as control . Macroscopic observationBoth halves of the frog hearts pretreated with and without Cd were soaked in a pH4 .0Ringer's solution (phthalate buffer) saturated with H2S for 10 minutes and were fixed in pure ethanol for more than 10 minutes. H2S reacted with Cd and yellow cadmium sulfide precipitates were formed in the tissue. Fig. 1 illustrates the macroscopic color difference between the control half (right) and Cd pretreated half (left) : the Cd pretreated heart ( Fig. 1-A) was more yellowish than the control (Fig. 1-B) distinctively . The color difference of staining between 0.1 mM Cd pretreated half and control half was discernible . These macroscopic observations suggested that Cd might bind with some structures of both atri um and ventricle. Microscopic observationSeveral histochemical techniques" were applied to the sectio ns of the hearts in order to examine the physiological assumption that cadmium binds with ca rdiac muscle fiber.The conditions (pH, concentration of staining solution) for chelati ng to obtain the largest *Present address: Department ot rhysiology,