Active Transport Of Potassium Ions Research Articles

Combination of glycemic and oxidative stress in lens: Implications in augmentation of cataract formation in diabetes

It is well known that the incidence of cataract is higher in diabetics as compared to non-diabetics. Its rate of maturation is also faster in the diabetics. The precise mechanism of this acceleration is not clearly understood. It is hypothesized that this could be a result of the combination of the metabolic and oxidative stress induced by glycemia itself with the age-associated increase in ambient generation of oxyradical species. In the current studies, we have investigated this possibility using the galactose cataract model. Galactosemia was induced by feeding rats a 50% galactose diet. The increased susceptibility of the glycemic lenses to physiological damage by reactive oxygen species (ROS) was studied by incubating them in Tyrode in the absence and presence of menadione. The resulting physiological damage to the lens was assessed initially in terms of its ability to maintain Na+–K+ ATPase dependent active transport of potassium ions, as represented by the uptake of rubidium ions. Subsequently, the level of ATP, indexing the general metabolic status, and the level of glutathione (GSH), indexing the status of antioxidant reserve, were also determined. The uptake of rubidium in the normal lenses incubated in the presence of the quinone was depressed to more than 50% of the controls run in the basal medium. A similar depression existed in the galactosemic lenses in comparison to the normal lenses. However, in the presence of menadione, the inhibition of the uptake was accentuated further in the case of galactosemic lenses, the uptake here being only 20% of the normal controls. Similarly, the galactosemic lenses were also more susceptible to menadione dependent decrease in ATP and GSH.

5'-p-fluorosulfonylbenzoyladenosine binds to the 28 kDa subunit of larval Manduca sexta midgut vacuolar-type ATPase.

ABSTRACT The larval lepidopteran midgut contains a mechanism for the active transport of potassium ions from blood to lumen (Harvey and Nedergaard, 1964). This insect K+ pump has been localized to the apical membrane of the midgut goblet cells (Dow et al. 1984). Recently it has been shown to consist of a proton-motive ATPase of the vacuolar class (V-ATPase) functioning in conjunction with a K+/ nH+ antiporter (Wieczorek et al. 1991).

STOMATAL RESPONSES TO 2,4‐DINITROPHENOL

SUMMARYThe effect of 2,4‐dinitrophenol (DNP) on stomatal movement in excised, turgid leaves of Stachytarpheta indica was investigated by microscopic examination of the abaxial epidermis. DNP prevented wide opening on illumination and closure in the dark, and affected concurrent changes in stomatal starch and potassium concentration in the guard cells. Carbon dioxide‐free air failed to reverse the DNP effect. The effect of DNP is attributed largely to its inhibition of hydrolysis of stomatal starch and of active transport of potassium ions to and from the guard cells. The possibility that DNP affects the energy supply for stomatal movements through its inhibition of oxidative phosphorylation is briefly discussed.

Diuresis in the cabbage white butterfly, Pieris brassicae: Fluid secretion by the malpighian tubules

The sudden weight loss at the pupal-adult ecdysis of the cabbage white butterfly, Peiris brassicae, is caused by a diuresis which greatly reduces the blood volume after emergence. Study of the Malpighian tubules as isolated preparations shows that only those of the adult insect possess the ability to secrete fluid at extremely fast rates when stimulated. In contrast to the fast-secreting tubules of bloodsucking insects, the mechanism of fluid secretion is not unusual, probably depending on the active transport of potassium ions.