Shikifumi Kitazawa

A simple method for the isolation of basolateral plasma membrane vesicles from rat kidney cortex Enzyme activities and some properties of glucose transport

A procedure for preparing basolateral membrane vesicles from rat renal cortex was developed by differential centrifugation and Percoll density gradient centrifugation, and the uptake of D-[3H] glucose into these vesicles was studied by a rapid filtration technique. (Na+ + K+)-ATPase, the marker enzyme for basolateral membranes, was enriched 22-fold compared with that found in the homogenate. The rate of D-glucose uptake was almost unaffected by Na+ gradient (no overshoot).

Effects of hardness on the disintegration time and the dissolution rate of uncoated caffeine tablets

The effects of hardness on disintegration and dissolution characteristics of uncoated caffeine tablets made at eight different pressure levels were studied. The disintegration times were determined using the J.P. VIII procedure with disks and the dissolution rate measurements were performed with the U.S.P. XVIII procedure (U.S.P. method) and the J.P. VIII disintegration test apparatus (J.P. method). A good correlation between the hardness and the disintegration times was obtained. The dissolution rate constants were determined from the equation of Noyes & Whitney (1897) and a good correlation between the hardness and the dissolution rate constants was obtained. The hardness governed the dissolution over all the stages from tablet to the smallest particles after the breakage by disintegration. The dissolution rates of the J.P. method were greater than those of the U.S.P. method.

Carrier-mediated transport of amino-cephalosporins by brush border membrane vesicles isolated from rat kidney cortex.

The uptake of cephalosporin antibiotics by brush border membrane vesicles isolated from rat renal cortex has been studied by a rapid filtration technique, demonstrating a carrier-mediated transport system for amino-cephalosporins such as cephalexin and cephradine. The antibiotics were taken up into an osmotically reactive intravesicular space. The uptake of cephalexin was saturable (apparent Km2.2 mM), was inhibited by structural analogues and sulfhydryl reagents, and was stimulated by the countertransport effect, although the Na+ gradient did not affect the uptake. This transport system was essentially different from the transport system for p-aminohippurate in brush border membranes. The uptake properties for cephradine in brush border membrane vesicles appeared to be similar to those for cephalexin. The present results suggest the existence of a carrier-mediated transport system for amino-cephalosporins in brush border membranes. This system may be a part of the mechanism of tubular reabsorption of these antibiotics.

Enzyme activities and sodium-dependent active d-glucose transport in apical membrane vesicles isolated from kidney epithelial cell line (LLC-PK1)

Apical membrane vesicles were isolated from the confluent LLC-PK1 cells by nitrogen cavitation and Mg/EGTA precipitation methods. The specific activities of marker enzymes for apical membranes were enriched 8- to 18-fold relative to those in the homogenate. D-[3H]Glucose uptake into the vesicles was stimulated in the presence of Na+ gradient (overshoot phenomenon), and the values of apparent Km and Vmax for Na+-dependent component of D-glucose uptake were 0.3 mM and 5.8 nmol/mg protein per min, respectively.

Interpretation of dissolution rate data from in vitro testing of compressed tablets

To find if theoretically and experimentally a relation existed between the dissolution rate theory of Kitazawa, Johno & others (1975) and that of Wagner (1969), a study was undertaken with uncoated caffeine, aspirin and proxyphylline tablets using two dissolution methods. Although the original treatment for surface area of drug available for dissolution was quite different between the two dissolution theories, the dissolution rate constants obtained were in fair agreement. Hence it might not be always necessary to take into consideration changes in the surface area as a function of dissolution rate, and the 1n W∞/ (W∞ ‐ W) versus time plot devised by Kitazawa & others might be a useful and simple means of obtaining the dissolution rate constant of an active ingredient from a dosage form such as compressed tablet.

A comparison of the dissolution rates of caffeine tablets in a rotating‐basket with those in a Sartorius dissolution tester

Uncoated caffeine tablets of four different hardnesses were tested for dissolution rate by the Sartorius (S.S. method) and by the rotating basket method of the U.S.P. XVIII. In both methods the dissolution rate decreased with increasing hardness, and the rate obtained with the S.S. method was always less than that by the U.S.P. method. This result cannot be explained as being due only to the difference in the volume of dissolution medium. Also it was difficult to ensure that the characteristic changes in the process of dissolution paralleled the curves obtained from a plot of % caffeine dissolved vs time. Accordingly, the dissolution rate constants were calculated from the slope of each straight line in a plot of In W∞/(W∞ ‐ W) vs time.