The effect of EDTA on the histochemical myofibrillar ATPase reaction

The effects of different salts and concentrations of ethylene diamine tetraacetic acid (EDTA) on the histochemically demonstrable myofibrillar ATPase reaction have been investigated. Serial frozen sections from the vastus lateralis muscle of rats, rabbits and guinea pigs were treated with cold (4 degrees) dipotassium EDTA solution and then incubated for myofibrillar ATPase activity. The results showed that all type I muscle fibres exhibited enhanced ATPase activity while type II fibres demonstrated either very low, moderate or intense reaction suggesting the existence of three different sub-populations. None of these effects was observed if the sections were immersed in magnesium chloride solution after preincubation in cold diK+ EDTA. Preincubation in cold non-ionic EDTA, disodium or tetrasodium EDTA did not affect the regular ATPase reaction pattern, while preincubation in warm (19 degrees--21 degrees C) solutions of the same salts resulted in reversal of the regular pattern of ATPase activity. The present histochemical data emphasise the importance of K+, Mg++ and temperature during preincubation of muscle fibres in EDTA before the demonstration of myofibrillar ATPase activity. Moreover, preincubation in a cold solution of diK+ EDTA may be valuable in the histochemical detection of distinct sub-populations of type II muscle fibres and certainly distinguished between type II white and type II red.