Abstract
During electrical stimulation of the frog neuromuscular preparation in Ringer solution, CaCl2 (1.8mM) was replaced by equimolar CoCl2 (Co-Ringer solution). Muscular contraction due to the motor nerve stimulation was blocked completely within 2min, while muscular contraction due to direct muscle stimulation was reduced but not completely blocked. The tissue was fixed with 2.5% glutaraldehyde prepared in Co-Ringer solution. After rapid wash in Ringer solution, the tissue was transfered into an aqueous solution containing 10mM K3Fe(CN)6 (precipitating agent of Co2+) and 90mM NaCl. In conventional transmission electron microscopy, large precipitates were observed close to both sides of the presynaptic membrane, outside of the sarcolemma in subsynaptic and extrasynaptic area, on the myofibrils and close to both sides of the membrane of the sarcoplasmic reticulum in the vicinity of the T-tubules. It is presumed that the sites where the precipitates were localized correspond to the voltage dependent calcium channels of the presynaptic membrane, sarcoplasmic membrane and membrane of sarcoplasmic reticulum. The precipitates found on the myofibrils are considerd as Co2+ which penetrated the endplate channels and directed towards the sarcoplasmic reticulum. To our knowledge, the present electron microscopic observation of Co2+ precipitatedwith potassium ferricyanide is the first attempt in the cobalt cytochemistry.
