Distribution and properties of an adenosine triphosphatase in the tanycyte ependyma of the IIIrd ventricle of the rat.

The distribution, histochemical properties and ultrastructural localization of adenosine triphosphate (ATP) hydrolyzing enzymes in the tanycyte ependyma of the third ventricle have been studied in female Wistar rats. Using a calcium-cobalt procedure and a lead capture technique, splitting of ATP could be demonstrated in perikarya and processes of tanycytes in the region of the ventromedial nucleus. The reaction showed no dependence on magnesium or sodium ions, did not occur with other monodi-, and tri-phosphates as substrates, and was inhibited by p-chlormercuribenzoate (PCMB) and sodium fluoride, but not by ouabain. With the calcium-cobalt method the highest intensity of reaction was found at pH 9.4, whereas the lead method gave optimal results at pH 6--8. At the ultrastructural level, the reaction product was found at the outer surface of the plasma membranes of tanycytes and reached its highest concentrations in the region of the region of the apical microvilli; From the findings it is concluded that splitting of ATP in tanycytes is due to a true ATPase. The enzyme might be involved in an active transport of substances by tanycytes.