Pineal and ependymal respiration with diverse substrates and inorganic ions

Abstract

Respiration of minced pineals and teased ependymal layers from ventricle IV of adult rats (Rattus norvegicus) was measured with standard Warburg apparatus and Krebs-Ringer-phosphate media. In studies of the effects of 13 substrates pineal O₂ uptake was greatest with succinate and glutamate; ependymal O₂ was greatest with glucose, pyruvate, mannose, and lactic acid. In isotonic media lacking substrate but with different Na:K ratios (total concentration = 150 mm), both tissues increased O₂ uptake as K concentration was increased from 0 to near 75 mm. At greater concentrations of K, O₂ uptake was reduced to a low level, above that when K was lacking, in ependyma, but significantly below even this level in pineal. Presence of glucose led to maximal O₂ uptake by both tissues with 125 mm Na and 19 mm K. Pineal respiration was not modified by changes in concentrations of Ca, Mg, PO₄, or Cu⁺⁺. Ependymal respiration was increased by small amounts of Ca, Mg, and increasing amounts of PO₄ (0–45 mm), and inhibited by Cu⁺⁺.