PubMed Health⌕ Search

Biomedical subjects

M G Brunette

Publications and source records attributed to M G Brunette.

At least 73 records · Page 4Linked to original sources
PubMed1982

Effects of L-bromotetramisole on phosphate transport by the proximal renal tubule: failure to demonstrate a direct involvement of alkaline phosphate.

Several recent studies have suggested that the alkaline phosphatase situated in the brush border membrane of the proximal convoluted tubule is positively related to inorganic phosphate reabsorption through this segment of the nephron. We examined this hypothesis by studying the influence of an inhibitor of alkaline phosphatase, L-bromotetramisole, upon phosphate transport through the isolated rabbit tubule, phosphate transport through brush border membrane vesicles of rats, and phosphate efflux from these vesicles. Results were compared with those obtained with D-bromotetramisole which is inactive on alkaline phosphatase. The microperfusion studies on isolated tubules did not show any significant influence of L-bromotetramisole on phosphate transport which slightly increased by 0.22 +/- 0.78 pmol . mm-1 . min-1 (NS). The experiments performed on brush border membrane vesicles indicated that at pH 7.5, both L- and D-bromotetramisole at a concentration of 0.1 mM slightly but significantly increased phosphate input from 1800 +/- 149 to 1999 +/- 157 and 1982 +/- 168 pmol/mg protein per 30-S incubation (P less than 0.01 and P less than 0.005, respectively). At pH 8.5, the same tendency was observed but was significant with the D isomer only. Finally, the effect of an increasing phosphate transport was accentuated when both isomers were tested at 1.0-mM concentration. Phosphate efflux from brush border membrane vesicles was not influenced by L- or D-bromotetramisole at 0.1 mM. At 1.0 mM, however, both isomers accelerated this release. These results do not support the hypothesis of a direct action of alkaline phosphate upon phosphate transport through the entire proximal convoluted tubule, nor upon input or output of this electrolyte through the brush border membrane vesicles. The two forms of bromotetramisole have variable effects upon phosphate transport which are unrelated to the alkaline phosphatase activity.

Alkaline Phosphatase↗
PubMed1981

Localization of immunoreactive vitamin D-dependent calcium binding protein in chick nephron.

Immunoreactive vitamin D-dependent calcium binding protein (iCaBP) has been localized in the chicken nephron, using microdissection and subsequent radioimmunoassay (RIA). Six to ten weeks old vitamin D-replete chicks were sacrificed and the kidneys removed. The various segments of the nephron, i.e. the proximal convoluted tubule (PCT), the thick part of the hairpin loops (thick loops), the thin part of the hairpin loops (thin loops), the distal convoluted tubules (DCT) and the cortical collecting tubules (CCT) were microdissected and grouped according to their morphological characteristics. Because the transition between DCT and CCT was not evident, these two segments were gathered together. The samples were assayed for iCaBP by a microradioimmunoassay, using antisera against the vitamin D-dependent chicken intestinal CaBP. iCaBP was localized in the thin loops and in the DCT-CCT segments (24.7 +/- 5 and 20.8 +/- 3 ng/mg protein, respectively). No iCaBP was detected either in the PCT using up to 32 micrograms protein, or in fragments of medullary papilla, assaying up to 4 micrograms protein.

Animals↗
PubMed1979

Hormone-sensitive adenylate cyclase along the nephron of genetically hypophosphatemic mice.

The response of the adenylate cyclase (AC) activity to PTH and calcitonin was measured along the nephron of normal (N) and mutant hypophosphatemic (Hyp) mice of the C 57 BL/6J strain, using in vitro single tubule AC microassay. In each experiment, a Hyp mouse was paired to a N mouse from the same litter. In the presence of PTH (10 U/ml), AC activities (femtomoles cAMP per millimeter of tubule per 30-min incubation) were reduced in the proximal convoluted tubule of Hyp mice as compared to N mice in all experiments (448 +/- (SEM) 46 vs. 831 +/- 79, N = 4, P less than 0.01). Some decrease in AC response to PTH also was noted in the cortical portion of the thick ascending limb of the loop of Henle (476 +/- 70 in Hyp mice vs. 719 +/- 83 in N mice, N = 4, P = NS). The Hyp and N AC responses to PTH were similar in the "bright" and "granular" portions of the distal convoluted tubule (1524 +/- 177 in Hyp mice and 1538 +/- 228 in N mice, N = 4). The other segments tested were not responsive to PTH (except the pars recta of the proximal tubule). In the presence of salmon calcitonin (10 ng/ml), a striking 5- to 12-fold increase in AC activity of the "bright" and "granular" portions of the distal convoluted tubule was observed in each Hyp mouse as compared to its paired N control (2434 +/- 618 vs. 399 +/- 56, N = 6, P less than 0.01). The AC response to calcitonin was also increased, though to a lesser extnet (Hyp/N = 1.8) in the "light" portion of the distal tubule (590 +/- 60 in Hyp and 352 +/- 36 in N mice, P less than 0.01). Other segments of the mouse nephron were also observed to contain calcitonin-sensitive AC, but the responses were of limited magnitude only and were not statistically different in Hyp and N mice. Dose-response curves showed that the decrease of the response to PTH in the proximal tubule as well as the increase of the response to calcitonin in the distal tubule were present in Hyp mice for the whole range of hormone concentrations tested. In both structures, the apparent Km for the cyclase activation by the hormone was similar in the Hyp and its paired N mouse.

Adenylyl Cyclases↗
PubMed1978

Magnesium handling by the papilla of the young rat.

In a recent study it was found that in Mg loaded rats, the fraction of filtered Mg (% E Mg) recovered in the bend of the loop of Henle of papilla was greater than the filtered load. However, the site of this Mg addition was unspecified and could be either the juxtamedullary proximal tubule, the pars recta, or in the papilla, the descending limb of the loop of Henle. In order to investigate the movement of Mg in the various structures of the papilla, we have studied: 1. The transport of this electrolyte along the collecting duct. 2. Its relative concentration in the loop of Henle and in the adjacent vasa recta. The experiments have been performed in hydropenic and Mg loaded rats. In the collecting duct, the inulin and Mg concentrations increase proportionally, indicating an absence of any transport of Mg along this part of this nephron. In the vasa recta of the accessible papilla, the capillary over peripheral plasma Mg ratio (C/UF Mg) in hydropenia and after Mg loading [1.88 +/- 0.15 (ES) and 2.89 +/- 0.25] were significantly lower than the corresponding TF/UF Mg in the adjacent loops of Henle (2.90 +/- 0.17 and 4.04 +/- 0.37). This finding reduces the possibilities of a Mg passive diffusion from the capillaries to the tubular lumen, unless the electrical potential of the descending limb is more negative than -5 mV. The hypothesis of an active secretion, or a passive diffusion of Mg in the deep proximal tubule, in the pars recta, or in the early non accessible descending limb constitutes the other alternative.

Animals↗
PubMed1975

Micropuncture study of renal magnesium transport in magnesium-loaded rats.

Mg transport in the deep loop of Henle was studied in 15 young rats (50-60 g) after acute systemic Mg loading (UFMg (ultrafilterable Mg) 4.77 meq/liter). Intratubular Mg was measured with a recently described fluorometric microtechnique. The mean values of the TF/P inulin and TF/UF Mg ratios were 3.32 +/- 0.13 and 4.25 +/- 0.17, respectively. The proportion of filtered Mg recovered in this part of the nephron was therefore 131.2 +/- 5.0%, indicating that an appreciable amount of Mg entered the lumen prior to the sites of puncture. A significant correlation between the TF/P inulin and TF/UF Mg ratios suggests that water reabsorption also contributes to the high concentration of Mg in the loop of Henle during systemic Mg loading. In another series of young rats (90-160 g), similarly loaded with MgCl2 (UFMg 5.81 meq/liter), Mg and inulin were measured in superficial proximal (PT) and distal tubules (DT). Punctures were paired at two sites of the same PT and DT. The Mg concentration increased progressively along the PT in such a way that 90.5% of the filtered load still remained in the late proximal loops. If superficial and deep proximal tubules behave in a similar manner, it may be concluded that the site of entry of Mg is located between the late accessible part of the PT and the bend of the loop of Henle. Only 58.0 +/- 3.0% of the filtered Mg was delivered to the DT, indicating that Mg is extensively reabsorbed in the ascending limb, despite systemic loading. The proportion of filtered Mg did not vary along the DT, indicating no net reabsorption.

Animals↗