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Abstract: Effects of treatment with thyroid hormones l-3,5,3′-tri-iodothyronine (T3) and l-thyroxine (T4) on oxidative energy metabolism in cerebral mitochondria from hypothyroid adult rats were examined. It was observed that T3 and T4 stimulated respiratory activity in a substrate-specific and dose-dependent manner. The results also suggest that the synthesis of cytochrome aa 3 and of cytochrome c may be dependent on both T3 as well as T4 whereas higher concentrations than normal of T3 and T4 may have a catabolic influence on cytochrome b content. [Copyright &y& Elsevier]

Abstract: Mitochondrial function is a key determinant of both excitability and viability of neurons. Present studies were carried out to decipher cerebral mitochondrial oxidative energy metabolism and membrane function in the chronic condition of generalized seizures induced by picrotoxin (PTX) in rats. PTX-induced convulsions resulted in decreased respiration rates (14–41%) with glutamate, pyruvate + malate, and succinate as substrate. The ADP phosphorylation rates were drastically reduced by 44–65%. An opposite trend was observed with ascorbate + N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) as substrate. In general, uncoupling of the mitochondrial electron transport was observed after PTX treatment. Malate dehydrogenase (MDH) and succinate dehydrogenase (SDH) activities were decreased by 20–80%; also, there was significant reduction in cytochrome b content after PTX treatment, while the FoF1 ATPase (complex V) activity increased in basal and 2,4-dinitrophenol (DNP)-stimulated condition, indicating increased membrane fragility. The substrate kinetics analysis had shown that Km and Vmax of the higher affinity kinetic component of ATPase increased significantly by 1.2- to 1.4-fold in epileptic condition. Temperature kinetic analysis revealed 1.2-fold increase in energies of activation with decreased transition temperature. The total phospholipid (TPL) and cholesterol (CHL) contents decreased significantly with lowering of diphosphatidylglycerol (DPG), phosphatidylethanolamine (PE), phosphatidylinositol (PI), and phosphatidylserine (PS), while lysophospholipid (lyso), sphingomyelin (SPM), and phosphatidylcholine components were found to be elevated. Brain mitochondrial membrane was somewhat more fluidized in epileptic animals. Possible consequences of mitochondrial respiratory chain (MRC) dysfunction are discussed. In conclusion, impairment of MRC function along with structural alterations suggests novel pathophysiological mechanisms important for chronic epileptic condition. [Copyright &y& Elsevier]

A simplified method for inorganic phosphate determination has been developed. The method is sensitive, easy, economic, and applicable for estimation of phosphate released in both enzymatic and nonenzymatic reactions. A mixture of hydrazine sulfate and ascorbic acid was used as the reducing agent and the conditions for the development of the molybdenum blue color were optimized. Thus in the 4.0 ml assay system, 0.4 ml of the reducing agent solution containing 20 mg each of hydrazine sulfate and ascorbic acid per milliliter of 1.0 N H2SO4 gave a rapid optimum color development with absorption maximum at 820 nm. Color development showed a linear relationship up to 10 μg Pi concentration. Thus the method has a 2.5 × higher range of Pi estimation than that of the Bartlett method. The molar extinction coefficient at 820 nm was higher than that obtained in the Bartlett procedure. Also the molybdenum blue color formed was stable up to 24 h. Under the standard assay conditions, interference from acid-labile phosphate as in the case of Na+,K+ ATPase was at the minimum. The applicability of the method for assay of microsomal Na+,K+ ATPase and glucose-6-phosphatase was checked in microassays (final volume 0.1 ml) in comparison to the conventional procedures which use 3–4 times higher volumes. Likewise the applicability of the method for phospholipid analysis was compared with that of the conventional Bartlett method. Under both test systems the results obtained by the micromethod were identical to those obtained by the conventional methods. In general the method, which rapidly produces quantitatively molybdenum blue color, not only is rapid economical, and convenient but also has wide applicability. [Copyright &y& Elsevier]