Effects of alloxan and ninhydrin on mitochondrial Ca2+ transport

Abstract

Alloxan at millimolar concentrations slightly inhibited the velocity of Ca2+ uptake by isolated rat liver mitochondria irrespective of the free Ca2+ concentration between 1 and 10 microM and was an effective concentration-dependent stimulator of mitochondrial Ca2+ efflux. Ninhydrin also slightly inhibited the velocity of mitochondrial Ca2+ uptake but only at free Ca2+ concentrations above 5 microM. However, ninhydrin was a strong stimulator of mitochondrial Ca2+ efflux even at micromolar concentrations, 10-50 times more potent than alloxan. The mitochondrial membrane potential was reduced 10-20% at most by alloxan and ninhydrin. Alloxan and ninhydrin also stimulated Ca2+ efflux from isolated permeabilized liver cells. When isolated intact liver cells had been pre-incubated with alloxan or ninhydrin before permeabilization of the cells the ability of spermine to induce mitochondrial Ca2+ uptake was abolished. Glucose provided the typical protection against the effects of alloxan on mitochondrial Ca2+ transport only in experiments with intact cells but not in experiments with permeabilized cells or isolated mitochondria. Therefore glucose protection is apparently due to inhibition of alloxan uptake into the cell. Glucose provided no protection against effects of ninhydrin under any of the experimental conditions. Thus both alloxan and ninhydrin are potent stimulators of Ca2+ efflux by isolated mitochondria but very weak inhibitors of the velocity of mitochondrial Ca2+ uptake. The direct effects of ninhydrin on mitochondrial Ca2+ efflux may contribute to the cytotoxic action of this agent whereas the direct effects of alloxan on mitochondrial Ca2+ transport require concentrations which are too high to be of relevance for the induction of the typical pancreatic B-cell toxic effects of alloxan. However, the effects on mitochondrial Ca2+ transport during incubation of intact cells which may result from the generation of cytotoxic intermediates during alloxan xenobiotic metabolism may well contribute to the pancreatic B-cell toxic effect of alloxan.

Serum Biochemical Altrations Following Alloxan- Induced Diabetes Mellitus in the Local Male Donkey

“…This action has been implicated in the alloxan diabetogenicity as well as the hypothesis of the role of reactive oxygen species (ROS) formation (Heikkila et al, 1976) as Udayakumar et al (2009) presented that one of the diabetes manifestations is the enhancement of liver enzyme, glucose 6-phosphatase activity, the key enzyme for the process of gluconeogenesis. Lenzen et al (1992) proposed an additional mechanism for alloxan-induced hyperglycemia which suggests that alloxan reacts with two sulfhydryl groups SH at the sugar binding side of glucokinase which is essential for glycolysis and proper insulin secretion leading to the creation of disulfide bonds and inhibition of enzyme. DNA of βcells is well established as a target of the rising ROS so fragmentations will take place in βcells exposure to alloxan (Sakurai and Ogiso, 1995).…”

“…Ca +2 influx may result from alloxan ability to depolarize βcells (Dean and Matthews, 1972). Depolarization of cell membrane enhances the opening of voltage-dpendent Ca +2 channels and increases Ca +2 entry into the cells (Lenzen et al, 1992).…”

Effect of Ethanolic Extract of Olive Leaves on Blood Glucose and Cholesterol Levels in Diabetic Rabbits

“…) ) E (Katsumata and Katsumata, 1990 Szkudelski, 2001;Park et al, 1995;Okamoto, 1985) . Lenzen et al, 1992) . Satoa et al, 2007…”