Inhibition of binding of [3H]metolazone to rat kidney membrane by stilbene disulfonates

Thiazide diuretics inhibit an electroneutral chloride and sodium reabsorptive transport pathway in the renal distal convoluted tubule. [3H]Metolazone binds with high affinity to the drug recognition site on the thiazide-sensitive ion transporter. The molecular nature of this transporter is currently unknown. This report examines whether stilbene disulfonates [4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) and 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS)], agents that have been used to identify other anion-transporting proteins, could be useful in the identification of the thiazide receptor. We found that high concentrations of DIDS or SITS were required to inhibit binding of [3H]metolazone to rat kidney membranes, with apparent IC50 values of 380 and 940 microM, respectively. The inhibition was due to a decrease in the number of binding sites without alteration in the affinity of the binding. The inhibition was not reversible, as judged by the inability of the inhibition to be reversed by removal of the DIDS or SITS from the membranes prior to equilibration with [3H]metolazone. Addition of 100 mM NaCl to the incubation medium did not protect the [3H]metolazone binding site from inhibition by DIDS. We infer that DIDS and SITS irreversibly inhibit binding of [3H]metolazone by reaction with the thiazide receptor at a site other than the anion-transporting site.

Solubilization of thiazide diuretic receptors from rat kidney membranes

Thiazide-type diuretics act at receptors to inhibit NaCl transport in the renal distal tubule. We solubilized high-affinity [3H]metolazone binding sites from rat kidney membranes with Triton X-100, which was more effective than several other detergents. Phosphatidylcholine and a mixture of proteinase inhibitors were needed to stabilize binding so that 57% of solubilized binding remained after 72 h at 4 degrees C. The affinities of solubilized (Kd = 11.4 +/- 0.5 nM) and membrane-bound receptors (Kd = 12.0 +/- 1.7 nM) were similar. The maximal number of binding sites/mg protein of solubilized receptors was 46 +/- 3% (n = 5) of membrane-bound receptors. Diuretics with a wide range of affinities had similar affinities for the solubilized and membrane-bound sites. Chloride inhibited and sodium stimulated the binding of [3H]metolazone to solubilized receptors, as they do with membrane-bound receptors. These studies demonstrate that, as judged by ligand binding, thiazide receptors can be solubilized in an active conformation and provide the basis for future purification and reconstitution.

[Left ventricle diastolic function in hypertensive patients and responses to captopril]

The LV diastolic function of 37 cases with primary hypertension were studied by measuring the diastolic filling blood stream at mitral orifice using pulsed Doppler echocardiography. 30/37 (81%) patients were found to have impaired LV diastolic function as compared with 30 normals of a group at similar age. After 4 weeks of oral captopril treatment in 20/37 patients, BP dropped in 19/20; LV diastolic function improved in 75-80%; left ventricular mass also regressed in 16/20 captopril treated patients (210 +/- 62 vs 171 +/- 46 g, P less than 0.01). It showed that captopril is not only effective in lowering blood pressure but also in improving the impaired LV diastolic function.

[Preparation of inside-out vesicles from red blood cell membranes and measurement for its Ca2+ uptake]

Sealed, inside-out red cell membrane vesicles (IOV) from rats were prepared by a modified method of Steck (1974). The preparation contained 70% of IOV. In the presence of ATP and Mg2+, these vesicles actively took up Ca2+ with a high efficiency and reproducibility. The intraassay coefficient of variance (C.V.) was 3.6% and the interassay C.V. was 13.58%. The active Ca2+ transport reached the maximal level in 10 minutes of incubation, and linearly correlated with the IOV concentration. The Ca2+ uptake rate in Wistar rats was 9.39 +/- 1.28 nmol/mg IOV protein/min. IOV rapidly lost Ca2+ when A23187 was added. The active transport was stimulated by calmodulin, and inhibited by trifluoperazine.

IgE synthesis by chronic lymphocytic leukemia cells

The present results indicate that B cells isolated from chronic lymphocytic leukemia (B-CLL) from 11 of 14 patients are capable of specifically producing IgE upon costimulation with IL-4 and hydrocortisone (HC). IgE is detected by intracytoplasmic fluorescence staining and by RIA. Clinical, hematological, and immunological parameters (including Rai stage, WBC, Lc, sIg kappa/lambda, CD5, and CD23 expression) cannot distinguish the IgE responder from the nonresponder patients. IL-4 alone is a potent inducer of human IgE synthesis by normal PBMC and we show here that its effect is strikingly enhanced by HC. The IgE produced by B-CLLs are monoclonal since they display the same L chain type as the freshly isolated CD5+ B-CLLs. We, therefore, conclude that the combination of IL-4 and HC can abrogate the maturation arrest of CD5+ B-CLLs by inducing their differentiation into IgE-producing cells. The present data provide a unique model to study the isotype switching to IgE and the regulation of human IgE synthesis by monoclonal human B cells.

Crystal structure and the equation of state of thorium monophosphide for pressures up to 50 GPa

High-pressure X-ray diffraction studies have been performed on ThP using synchrotron radiation and a diamond-anvil cell. The bulk modulus B 0 and its pressure derivative B′0 have been determined (B 0 = 137 GPa; B′0 = 5.1). A phase transition from the NaCl structure to the CsCl structure was observed at about 30 GPa.