Effects of calcium-EGTA buffers on active calcium transport in inside-out red cell membrane vesicles.

In inside-out red cell membrane vesicles, the free calcium concentration half-maximally stimulating active calcium uptake is about 2 orders of magnitude smaller in a calcium-EGTA buffer than in media containing unbuffered calcium. In calcium-EGTA buffer, the maximum rate of calcium uptake is determined by the total calcium concentration present. A possible model for explaining these findings is presented.     

Scanning-autoradiography--a new method for the demonstration of membrane-surface-associated structures.

A method for the demonstration of membrane-localized markers and receptors is described which results from the combination of autoradiography and scanning electronmicroscopy.     

The renal concentrating ability of newly born Brattleboro rats (hereditary diabetes insipidus).

In Brattleboro rats, there was no difference in urine osmolality between animals with and without diabetes insipidus after water deprivation up to age 14 days, and it appeared at age 18 days due to increase of osmolality in non-diabetic individuals.     

Characterization of D-fructose transport by rat kidney brush-border membrane vesicles: changes in hypertensive rats

D-fructose transport was characterized in renal brush-border membrane vesicles (BBMVs) from both spontaneously hypertensive rats (SHR) and normotensive genetic control Wistar-Kyoto (WKY) rats. Kinetic studies indicated that the maximal rate (Vmax) of D-fructose transport was significantly lower in SHR compared with WKY rats. No differences were observed in the Michaelis constant (Km) or the diffusion constant (Kd) between the two groups of animals. D-fructose inhibited its own transport, whereas the presence of D-glucose, D-galactose, phlorizin, and cytochalasin B did not inhibit the transport of D-fructose in either animal group. To explain the reduction in D-fructose transport in SHR, the density of the D-fructose transporter, GLUT5, was analyzed by Western blot. GLUT5 levels were lower in SHR, a reduction similar to that of the Vmax. Thus, there appears to be a high-affinity, low-capacity, GLUT5-type fructose carrier in the apical membranes of rat kidney cortex, and the decrease in the Vmax of D-fructose transport in renal BBMVs from hypertensive rats correlates well with a reduction in the expression of GLUT5 protein.