Search PubMed⌕ Search

Biomedical subjects

G Ritchie

Publications and source records attributed to G Ritchie.

33 records · Page 2Linked to original sources
PubMed1998

Mg2+/Ca2+ sensing inhibits hormone-stimulated Mg2+ uptake in mouse distal convoluted tubule cells.

The distal convoluted tubule plays a significant role in renal magnesium conservation. An immortalized mouse distal convoluted tubule (MDCT) cell line has been extensively used to study the cellular mechanisms of magnesium transport in this nephron segment. MDCT cells possess an extracellular polyvalent cation-sensing mechanism responsive to Mg2+, Ca2+, and neomycin. The present studies determined the effect of Mg2+/Ca2+ sensing on hormone-mediated cAMP formation and Mg2+ uptake in MDCT cells. MDCT cells were Mg2+ depleted by culturing in Mg2+-free media for 16 h, and Mg2+ uptake was measured by microfluorescence after placing the depleted cells in 1.5 mM MgCl2. The mean rate of Mg2+ uptake was 164 +/- 5 nM/s in control MDCT cells. Activation of Mg2+/Ca2+ sensing with neomycin did not affect basal Mg2+ uptake (155 +/- 5 nM/s). We have previously reported that treatment of MDCT cells with either glucagon or arginine vasopressin (AVP) stimulated Mg2+ entry. In the present studies, the addition of extracellular Mg2+ or Ca2+ inhibited glucagon- and AVP-stimulated cAMP formation and Mg2+ uptake in concentration-dependent manner with half-maximal concentrations of approximately 1.5 and 3.0 mM, respectively. Exogenous cAMP or forskolin stimulated Mg2+ uptake in the presence of Mg2+/Ca2+ sensing activation. We infer from these studies that Mg2+/Ca2+-sensing mechanisms located in the distal convoluted tubule may play a role in control of distal magnesium absorption.

Amiloride↗
PubMed1998

PGE2 stimulates Mg2+ uptake in mouse distal convoluted tubule cells.

Prostaglandins have diverse effects on renal electrolyte reabsorption, inhibiting NaCl absorption in the thick ascending limb and modulating sodium and calcium transport in cortical collecting cells. It is unclear what effect, if any, prostaglandins have on tubular magnesium handling. The effects of prostaglandin E2 (PGE2) were studied on immortalized mouse distal convoluted tubule (MDCT) cells by measuring cellular cAMP formation with radioimmunoassays and Mg2+ uptake with fluorescence techniques. Intracellular free Mg2+ concentration ([Mg2+]i) was measured on single MDCT cells using microfluorescence with mag-fura 2. To assess Mg2+ uptake, MDCT cells were first Mg2+ depleted to 0.22 +/- 0.01 mM by culturing in Mg2+-free media for 16 h and then placed in 1.5 mM MgCl2, and the changes in [Mg2+]i were determined. [Mg2+]i returned to basal levels, 0.53 +/- 0.02 mM, with a mean refill rate, d([Mg2+]i)/dt, of 173 +/- 8 nM/s. Indomethacin, 5 microM, diminished basal Mg2+ uptake, suggesting that endogenous prostaglandins may stimulate Mg2+ entry in control cells. PGE2 stimulated Mg2+ entry in a concentration-dependent manner with maximal response of 311 +/- 12 nM/s, at a concentration of 10(-7) M, which represented an 80 +/- 3% increase in uptake rate above control values. This was associated with a sixfold increase in intracellular cAMP generation. PGE2-stimulated Mg2+ uptake was completely inhibited with the Rp diastereoisomer of adenosine 3',5'-cyclic monophosphothionate (Rp-cAMPS), a protein kinase A inhibitor, and U-73122, a phospholipase C inhibitor, and partially by chelerythrine, a protein kinase C inhibitor. Accordingly, PGE2-mediated Mg2+ entry rates involve multiple intracellular signaling pathways. These studies demonstrate that PGE2 stimulates Mg2+ uptake in a cell line of MDCT.

Animals↗
PubMed1996

Na+/Ca2+ exchanger in epithelial cells of the porcine cortical thick ascending limb.

Intracellular Ca2+ concentration ([Ca2+]i) plays an important role in the signal transduction processes within cortical thick ascending limb (CTAL) cells. Control of [Ca2+]i was investigated in isolated CTAL cells with microfluorescent techniques. CTAL cells pretreated with ouabain to elevate intracellular Na+ concentration ([Na+]i) had basal [Ca2+]i of 86 +/- 2 nM. Removal of extracellular Na (Nao+) or voltage depolarization with KCl (in the presence of Nao+) resulted in a rapid and reversible maximal elevation of [Ca2+]i (1,023 +/- 72 nM, n = 28), which was dependent on the presence of external Ca2+ (Cao2+). The rise in [Ca2+]i was inhibited with La3+, Mg2+, amiloride, and bepridil. The increments of [Ca2+]i with either removal of Nao+ or voltage depolarization were dependent on pretreatment with ouabain and increases in [Na+]i. The presence of a Na+/Ca2+ exchanger was, confirmed with hybridization techniques, and the isoform was identified by sequencing the alternative splicing site within the intracellular loop. A gene transcript that encodes a portion of the intracellular loop of the renal Na+/Ca2+ exchanger was amplified from cortical tissue and single CTAL cells by reverse transcription-polymerase chain reaction, using primers flanking the alternative splicing site. Southern hybridization and DNA sequencing demonstrated the isoform contained exons B and D, which is characteristic of one isoform (NACA3) of the renal Na+/Ca2+ exchanger. The results provide both functional and molecular evidence for a Na+/Ca2+ exchanger in thick ascending limb cells of the porcine kidney.

Animals↗
PubMed1996

Modulation of Na+/Ca2+ exchange in epithelial cells of porcine thick ascending limb.

We have provided functional and molecular evidence for the presence of Na+/Ca2+ exchange in isolated porcine cortical thick ascending limb (CTAL) cells. The present studies were designed to show that this exchange activity may be modulated by phosphorylative processes. Control of intracellular Ca2+ concentration ([Ca2+]i) was determined in isolated CTAL cells with microfluorescence. CTAL cells were pretreated with ouabain to elevate intracellular Na+ concentration ([Na+]i) from 10 to 20 mM. These cells had normal basal [Ca2+]i (79 +/- 3 nM). Substitution of extracellular NaCl (50 mM) with KCl resulted in the rapid elevation of [Ca2+]i to maximal levels of 795 +/- 60 nM (n = 17). The increments of [Ca2+]i were associated with [Na+]i. We next determined the modulation of Na+/Ca2+ exchange activity with phosphorylative inhibitors. Pretreatment of cells with calmidazolium, a Ca(2+)-calmodulin inhibitor, resulted in a shift of the [Na+]i dependence curve to the right. Pretreatment with okadaic acid, a phosphatase 1 and 2A inhibitor, increased the Na+/Ca2+ exchanger activity resulting in half-maximal [Ca2+]i increase near normal [Na+]i of 12 mM. Furthermore, in the presence of okadaic acid in normal CTAL cells, pretreatment with ouabain and the elevation of [Na+]i was not required to elicit increments in [Ca2+]i. These data indicate that Na+/Ca2+ exchange is present in CTAL cells and the exchange activity appears to be modulated, directly or indirectly, by phosphorylation events.

Animals↗
PubMed1991

Inhibition of sodium-phosphate cotransport in renal brush-border membranes with the stilbenedisulfonate, H2-DIDS.

Membrane proteins involved with sodium/phosphate cotransport across the renal brush border provide the sensitive control for phosphate homeostasis. The present study describes the inhibition of sodium/phosphate cotransport with the stilbenedisulfonate derivatives, DIDS and H2-DIDS. Preincubation of the rat brush-border membrane vesicles with H2-DIDS led to the inhibition of sodium-dependent phosphate uptake with a half maximal concentration, IC50, of about 10 microM. The inhibition was irreversible supporting the notion that H2-DIDS forms covalent bonds with the cotransporter. The cotransporter could be protected by excess sodium phosphate but not sodium chloride, sodium sulfate, sodium succinate, sodium bicarbonate, nor sodium phosphonoformate. These observations suggest that the stilbenedisulfonates may be useful in labeling the sodium/phosphate cotransporter within renal brush-border membranes.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1991

Some characteristics of sodium-independent phosphate transport across renal basolateral membranes.

Sodium-independent phosphate transport was evaluated in porcine renal basolateral membrane vesicles. Phosphate uptake was saturable with an apparent Km 10.1 +/- 1.2 mM and Vmax 13.6 +/- 2.0 nmol (mg protein)-1 min-1, n = 5. Phosphate uptake was trans-stimulated with intravesicle phosphate and was enhanced with a positive transmembrane electrical potential. Arsenate and bicarbonate inhibited phosphate transport but other anions including sulfate and phosphonoformate were without effect. These studies indicate that phosphate uptake across basolateral membranes is present in the absence of sodium, is facilitated, and is specific for phosphate. The apparent affinity and rate of phosphate transport across the basolateral membrane is significantly higher than the respective parameters observed for the brush-border membrane.

Animals↗
PubMed1989

Digital image display station performance requirements based on physician experience with a prototype system.

The authors report on observations of and interviews with physicians using a prototype digital image display and reporting station. While the users generally agree that image quality is clinically satisfactory, they are unanimous in their opinion that improvements in the man-machine interface are required before case review by this mechanism is clinically acceptable in a production environment. A model image and information user interface is presented. It was developed in answer to the needs of radiologists and referring physicians operating in the imaging department of a community acute-care facility. In such an environment images and related information must be communicated quickly and often simultaneously to different parts of the department and hospital. The user interface with the management system and the management system itself must address the varied functions and the needs of both the medical and clerical staff. Image enhancement processes, for example, must be restricted to those that quickly provide significantly more perceivable diagnostic information. Little-used processes that may occupy significant portions of the display and the console's computing power must be trimmed or eliminated.

Computer Systems↗
PubMed1989

The perception of poverty and wealth among teenage university students.

This study is concerned with the perception of poverty and wealth among teenage university students. Two hundred twenty students completed a questionnaire which probed their perceptions of the attributions and consequences of poverty and wealth, requested them to estimate the job prospects of a school leaver with and without a certificate qualification, and also requested that they estimate the income for both a specified "poor" and "rich" man. The students also provided information about their economic preferences, religious position, and family financial position. Results indicate that the sample emphasized the significance of the family and placed little weight on luck when dealing with poverty and wealth. The sample emphasized the economic consequences of poverty and wealth, and did not rate their psychological consequences as being of much importance. Certain groups within the sample showed some deviations in their perceptions. The most substantial group differences were between the capitalist-religious and socialist-religious groups.

Adolescent↗
PubMed1988

A serendipitous isolate of Histoplasma capsulatum.

This is a report of an unexpected laboratory diagnosis of Histoplasma capsulatum. The fungus was isolated from an acute cellulitic lesion on the forearm of an elderly male patient with a functioning renal transplant. The patient resides within the environs of Brisbane and has not travelled outside Australia. We consider the isolation of H. capsulatum from a rare site in a patient resident in a non-endemic area indicative of a latent opportunistic infection in an immunocompromised patient.

Histoplasma↗
PubMed1985

A microcomputer based controller for neuromuscular block during surgery.

A microcomputer based control system has been developed to automatically induce and maintain neuromuscular block during surgery. The system repeatedly adjusts the infusion rate of a muscle relaxant, succinylcholine, based on the evoked, rectified, and integrated electromyogram (EMG). The system was tested in 12 patients for a 30-min infusion period with a setpoint of 80% depression of the evoked, rectified, and integrated thenar EMG. The mean time to reach the setpoint for 10 of the patients was 5.5 (+/- 1.87 SD) min and the mean time for 95% recovery after infusion was stopped was 5.4 (+/- 0.83 SD) min. Average overshoot was 9.9% of the baseline (+/- 3.1% SD), and the average time within +/- 10% of the setpoint was 22.1 min (+/- 7.26 SD). The total dose of succinylcholine for these 10 patients ranged from 1.21 to 3.77 mg/kg with a mean of 1.92 mg/kg. The other two patients were relatively insensitive to the drug and the controller was unable to bring the response to the setpoint due to a ceiling placed on infusion rate by the control algorithm.

Computers↗
PubMed1979

Cystic chromomycosis of the skin.

Five patients with solitary cystic granulomatous lesions of the skin are described. Wood splinters and brown pigmented fungal elements were present in all 5 cases. "Cystic chromomycosis" is suggested as an appropriate title to avoid confusion with the cutaneous verrucous form, chromoblastomycosis.

Adolescent↗
PubMed1978

Pseudomyxoma peritonei et ovarii with an occult neoplasm of appendix: case report.

Although pseudomyxoma peritonei is comparatively rare, the simultaneous occurrence in this condition of mucinous tumours of ovary and appendix is common and has been termed pseudomyxoma peritonei ovarii et appendicis. Four closely followed patients in a small series showed only 25% 6-year survival. This paper presents a further case with a 14-month follow-up.

Appendiceal Neoplasms↗