Evidence of Electron Heating by Alpha Particles in JET Deuterium-Tritium Plasmas.

The fusion-born alpha particle heating in magnetically confined fusion machines is a high priority subject for studies. The self-heating of thermonuclear fusion plasma by alpha particles was observed in recent deuterium-tritium (D-T) experiments on the joint European torus. This observation was possible by conducting so-called "afterglow" experiments where transient high fusion yield was achieved with neutral beam injection as the only external heating source, and then termination of the heating at peak performance. This allowed the first direct evidence for electron heating of plasmas by fusion-born alphas to be obtained. Interpretive transport modeling of the relevant D-T and reference deuterium discharges is consistent with the alpha particle heating observation.

Lost alpha Faraday cup foil noise characterization during Joint European Torus plasma post-processing analysis.

Capacitive plasma pickup is a well-known and difficult problem for plasma-facing edge diagnostics. This problem must be addressed to ensure an accurate and robust interpretation of the real signal measurements vs noise. The Faraday cup fast ion loss detector array of the Joint European Torus (JET) is particularly prone to this issue and can be used as a testbed to prototype solutions. The issue of separation and distinction between warranted fast ion signal and electromagnetic plasma noise has traditionally been solved with hardware modifications, but a more versatile post-processing approach is of great interest. This work presents post-processing techniques to characterize the signal noise. While hardware changes and advancements may be limited, the combination with post-processing procedures allows for more rapid and robust analysis of measurements. The characterization of plasma pickup noise is examined for alpha losses in a discharge from JET's tritium campaign. In addition to highlighting the post-processing methodology, the spatial sensitivity of the detector array is also examined, which presents significant advantages for the physical interpretation of fast ion losses.

An arc control and protection system for the JET lower hybrid antenna based on an imaging system.

Arcs are the potentially most dangerous events related to Lower Hybrid (LH) antenna operation. If left uncontrolled they can produce damage and cause plasma disruption by impurity influx. To address this issue an arc real time control and protection imaging system for the Joint European Torus (JET) LH antenna has been implemented. The LH system is one of the additional heating systems at JET. It comprises 24 microwave generators (klystrons, operating at 3.7 GHz) providing up to 5 MW of heating and current drive to the JET plasma. This is done through an antenna composed of an array of waveguides facing the plasma. The protection system presented here is based primarily on an imaging arc detection and real time control system. It has adapted the ITER like wall hotspot protection system using an identical CCD camera and real time image processing unit. A filter has been installed to avoid saturation and spurious system triggers caused by ionization light. The antenna is divided in 24 Regions Of Interest (ROIs) each one corresponding to one klystron. If an arc precursor is detected in a ROI, power is reduced locally with subsequent potential damage and plasma disruption avoided. The power is subsequently reinstated if, during a defined interval of time, arcing is confirmed not to be present by image analysis. This system was successfully commissioned during the restart phase and beginning of the 2013 scientific campaign. Since its installation and commissioning, arcs and related phenomena have been prevented. In this contribution we briefly describe the camera, image processing, and real time control systems. Most importantly, we demonstrate that an LH antenna arc protection system based on CCD camera imaging systems works. Examples of both controlled and uncontrolled LH arc events and their consequences are shown.

Effects of magnetic shear on toroidal rotation in tokamak plasmas with lower hybrid current drive.

Application of lower hybrid (LH) current drive in tokamak plasmas can induce both co- and countercurrent directed changes in toroidal rotation, depending on the core q profile. For discharges with q(0) <1, rotation increments in the countercurrent direction are observed. If the LH-driven current is sufficient to suppress sawteeth and increase q(0) above unity, the core toroidal rotation change is in the cocurrent direction. This change in sign of the rotation increment is consistent with a change in sign of the residual stress (the divergence of which constitutes an intrinsic torque that drives the flow) through its dependence on magnetic shear.

Hypertrophy and hyperplasia of abdominal adipose tissues in women.

OBJECTIVE: To examine the expression of selected transcription factors involved in adipogenesis and genes related to lipid metabolism in abdominal subcutaneous and omental fat tissue. RESEARCH DESIGN AND METHODS: We obtained subcutaneous and omental adipose tissue samples from 40 women undergoing abdominal hysterectomies (age: 47+/-5 years; BMI 27.9+/-5.3 kg/m(2)). We measured isolated adipocyte size and metabolism, and detailed measures of body fat accumulation and body fat distribution were obtained (dual-energy X-ray absorptiometry and computed tomography, respectively). RESULTS: Adipocyte size of both subcutaneous and omental fat were increased with higher body fat mass values, with similar regression slopes in each compartment. In contrast, with higher body fat mass values, fat accumulation was progressively higher in the subcutaneous than in the visceral fat compartment, suggesting hyperplasia in the subcutaneous fat compartment. Messenger RNA levels of CEBPalpha, PPARgamma2, SREBP1c and genes related to lipid metabolism (LPL, FABP4, DGAT1, DGAT2, PLIN and HSL) were significantly higher in subcutaneous than in omental fat tissue (P< or =0.001 for all). Only subcutaneous expression of these genes tracked with obesity levels as reflected by significant positive associations between subcutaneous fat CEBPalpha, SREBP1c and DGAT2 expression and total body fat mass (r=0.37, r=0.41, r=0.57, respectively, P< or =0,05), fat percentage (r=0.40, r=0.39, r=058, respectively, P< or =0,05) and subcutaneous adipose tissue area (r=0.36, r=0.38, r=0.58, respectively, P< or =0,05). Omental adipose tissue expression levels of these genes were not significantly related to adiposity measures. CONCLUSIONS: These results show that in obese women, hyperplasia is predominant in the subcutaneous fat depot, whereas fat cell hypertrophy is observed both in the omental and subcutaneous compartments.

Increased expression of matrix metalloproteinase-9 in the eutopic endometrial tissue of women with endometriosis.

BACKGROUND: Endometriosis is a disease where endometrial tissue implants in ectopic locations. Remodelling of the extracellular matrix (ECM) is a prerequisite for the implantation of this tissue to be possible. METHODS: In this study, we detected immunoreactive matrix metalloproteinase-9 (MMP-9) throughout endometrial tissue and identified von Willebrand factor (vWF)-positive endothelial cells, CD45-positive leukocytes, CD3-positive T lymphocytes and CD68-positive macrophages as cells expressing MMP-9 in the stroma. RESULTS: We found an increased expression of MMP-9 in the uterine endometrial tissue of women with endometriosis, as assessed by zymography and enzyme-linked immunosorbent assay (ELISA) (P < 0.05). However, RT-PCR did not show a statistically significant increase in MMP-9 mRNA expression in these tissues (P = 0.14). There was no significant difference between women with and without endometriosis in the expression of tissue inhibitor of MMPs (TIMP)-1, a known natural inhibitor of the pro- and active forms of MMP-9, whether tested by ELISA or by RT-PCR (P = 0.46 and 0.37, respectively). Interestingly, the ratio of MMP-9/TIMP-1 expression was significantly higher in women with endometriosis than in normal women both at the protein and the mRNA levels (P < 0.05). CONCLUSION: These findings make plausible the involvement of MMP-9/TIMP-1 imbalance in the invasiveness of the endometrial tissue of patients with endometriosis and the ectopic development of the disease.

Increased soluble interleukin-1 receptor type II proteolysis in the endometrium of women with endometriosis.

Numerous functional changes were observed in the intrauterine endometrial tissue of women with endometriosis. Our previous studies revealed a marked decrease in the expression of interleukin-1 receptor type 2 (IL-1RII), a decoy receptor known for its ability to buffer IL-1 effects. The aim of the present study was to assess whether post-translational mechanisms such as proteolysis may contribute to the down-regulation of IL-1RII levels. Our data showed that soluble IL-1RII (sIL-1RII) concentrations released by freshly cultured endometrial tissue were significantly lower in women with endometriosis than in normal women (P < 0.01) and further revealed a statistically significant correlation between increased proteolysis and decreased sIL-1RII levels (P < 0.05; r = -0.47). (125)I-labelled soluble recombinant human IL-1RII ([(125)I]srhIL-1RII) was significantly more degraded in culture supernatant of tissues from women with endometriosis compared to normal women (P < 0.05), and natural tissue inhibitor of matrix metalloproteinase (TIMP)-1 inhibited [(125)I]srhIL-1RII degradation. Incubation of srhIL-1RII with active rhMMP-9 resulted in a dose-dependent degradation of srhIL-1RII as analysed by western blotting. Dual immunofluorescence showed an increased immunostaining for matrix metalloproteinase-9 in situ in the endometrial tissue of women with endometriosis compared to normal women and a decreased immunostaining for IL-1RII. The present study showed a reduced release of sIL-1RII by the endometrial tissue of women with endometriosis and revealed a proteolytic post-translational mechanism which may be involved in the down-regulation of IL-1RII levels. This may enhance IL-1-mediated activation of endometrial cells and contribute to the local immuno-inflammatory process observed in endometriosis patients.

Evidence for an increased release of proteolytic activity by the eutopic endometrial tissue in women with endometriosis and for involvement of matrix metalloproteinase-9.

BACKGROUND: For the implantation of endometrium in ectopic locations, remodelling of the extracellular matrix (ECM) is necessary. Many studies have shown an increased expression of various proteases in the ectopic endometrium of women with endometriosis. Few, however, have addressed possible changes in protease expression in the eutopic endometrium. METHODS AND RESULTS: Herein, we reveal an increased release of proteolytic activity by the eutopic endometrium of women with endometriosis compared with normal women (P < 0.01). Using zymography and western blotting, we identified matrix metalloproteinase (MMP)-2 and MMP-9 in the culture medium, and further found that MMP-9 secretion, as assessed by zymography and enzyme-linked immunosorbent assay (ELISA), was elevated in women with endometriosis compared with normal women (P < 0.05). No statistically significant difference in MMP-2 secretion between women with and without endometriosis was noted. However, a significant difference in the levels of the tissue inhibitor of metalloproteinases (TIMP)-1, a known MMP-9 inhibitor, was found (P < 0.05). CONCLUSION: The endometriosis-associated increase in proteolysis and imbalance between the secretion of MMP-9 and that of its natural inhibitor, TIMP-1, revealed in the culture medium of endometrial tissue may reflect in vivo the enhanced capacity of this tissue to break down the ECM in host tissues, thereby favouring its ectopic implantation and development.

Characterization of three types of calcium channel in the luminal membrane of the distal nephron.

We previously reported a dual kinetics of Ca2+ transport by the distal tubule luminal membrane of the kidney, suggesting the presence of several types of channels. To better characterize these channels, we examined the effects of specific inhibitors (i.e., diltiazem, an L-type channel; omega-conotoxin MVIIC, a P/Q-type channel; and mibefradil, a T-type channel antagonist) on 0.1 and 0.5 mM Ca2+ uptake by rabbit nephron luminal membranes. None of these inhibitors influenced Ca2+ uptake by the proximal tubule membranes. In contrast, in the absence of sodium (Na+), the three channel antagonists decreased Ca2+ transport by the distal membranes, and their action depended on the substrate concentrations: 50 microM diltiazem decreased 0.1 mM Ca2+ uptake from 0.65 +/- 0.07 to 0.48 +/- 0.06 pmol. microg-1.10 s-1 (P < 0.05) without influencing 0.5 mM Ca2+ transport, whereas 100 nM omega-conotoxin MVIIC decreased 0.5 mM Ca2+ uptake from 1.02 +/- 0.05 to 0.90 +/- 0.05 pmol. microg-1.10 s-1 (P < 0.02) and 1 microM mibefradil decreased it from 1.13 +/- 0.09 to 0.94 +/- 0.09 pmol. microg-1.10 s-1 (P < 0.05); the latter two inhibitors left 0.1 mM Ca2+ transport unchanged. Diltiazem decreased the Vmax of the high-affinity channels, whereas omega-conotoxin MVIIC and mibefradil influenced exclusively the Vmax of the low-affinity channels. These results not only confirm that the distal luminal membrane is the site of Ca2+ channels, but they suggest that these channels belong to the L, P/Q, and T types.

JET quasistationary internal-transport-barrier operation with active control of the pressure profile.

Quasistationary operation has been achieved on the Joint European Torus tokamak in internal-transport-barrier (ITB) scenarios, with the discharge time limited only by plant constraints. Full current drive was obtained over all the high performance phase by using lower hybrid current drive. For the first time feedback control on the total pressure and on the electron temperature profile was implemented by using, respectively, the neutral beams and the ion-cyclotron waves. Although impurity accumulation could be a problem in steady state ITBs, these experiments bring some elements to answer to it.

Observation of zero current density in the core of jet discharges with lower hybrid heating and current drive.

Simultaneous current ramping and application of lower hybrid heating and current drive (LHCD) have produced a region with zero current density within measurement errors in the core ( r/a< or =0.2) of JET tokamak optimized shear discharges. The reduction of core current density is consistent with a simple physical explanation and numerical simulations of radial current diffusion including the effects of LHCD. However, the core current density is clamped at zero, indicating the existence of a physical mechanism which prevents it from becoming negative.

Roles of ATP and cytoskeleton in the regulation of Na+/H+ exchanger along the nephron luminal membrane.

Although in LLC-PK cells ATP depletion has been shown to result in alterations of cytoskeleton actin and an inhibition of Na+/H+ exchanger activity, there is little information concerning the regulation of this exchanger in the distal luminal membrane by ATP and actin filaments. The present study examined the direct effect of ATP and cytochalasin B on the Na+/H+ exchanger activity in the proximal and distal tubule luminal membranes. The presence of 100 microM ATP in the luminal membrane vesicles from rabbit proximal tubules did not influence the Ethyl Isopropyl Amiloride sensitive Na+ uptake by these membranes. In contrast, the same treatment of luminal membranes from distal tubules significantly enhanced the exchanger activity from 0.22 +/- 0.04 to 0.39 +/- 0.08 pM/microg/10 sec (P < 0.02). When ATP was replaced by its nonhydrolysable form, ATPgammas, the effect on the distal luminal membrane was strongly diminished suggesting that the action of the nucleotide implicates a phosphorylation step. Confirming this hypothesis, addition of 300-microM-Rp cAMP, a protein kinase A inhibitor, completely abolished the effect of ATP. In view of the fact that a tight relationship has been described between ATP, the cytoskeleton complex and the exchanger activity, we studied the effect of cytochalasin B on this activity. The presence of 20 microM cytochalasin B in the distal luminal membrane vesicles induced, as observed with ATP, a significant increase in the Na+ uptake. However, the actions of ATP and cytochalasin B were not additive. These results suggest that firstly, ATP and short actin filaments of the cytoskeleton regulate the distal luminal isoform through an intramembranous mechanism and secondly, a phosphorylation mechanism is, at least partially, implicated in the action of ATP. In contrast, the proximal tubule exchanger is regulated through different mechanisms.

G proteins regulate calcium channels in the luminal membranes of the rabbit nephron.

The filtered calcium (Ca2+) is reabsorbed by the luminal membrane of the proximal and distal nephron. Ca2+ enters cells across apical plasma membranes along a steep electrochemical gradient, through Ca2+ channels. Regulation by various hormones implies several steps, including binding of these hormones to the basolateral membrane, interaction with G proteins, liberation of messengers, activation of kinases and finally opening of the channels at the opposite pole of the cells. In the present study, we examined whether the Ca2+ entry through the luminal membranes of proximal and distal tubules is also regulated by G proteins, by a membrane-limited process. Luminal membranes were purified from rabbit proximal and distal tubule suspensions, and their vesicles were loaded with GTPgammas or the carrier. Then, the 45Ca2+ uptake by these membrane vesicles was measured in the presence and absence of 100 mM NaCl. In the absence of Na+, intravesicular GTPgammas significantly enhanced 0.5 mM Ca2+ uptake by the proximal membrane vesicles from 0.53 +/- 0.06 to 0.72 +/- 0.06 pmol/microg/10 s (p < 0.05). In the presence of Na+, however, this effect disappeared. In the distal tubules, intravesicular GTPgammas increased 0.5 mM Ca2+ uptake in the absence (from 0.57 +/- 0.02 to 0.79 +/- 0.02 pmol/microg/10 s, p < 0.02) and in the presence (from 0.36 +/- 0.03 to 0.55 +/- 0.03 pmol/microg/10 s, p < 0.02) of Na+. The action of GTPgammas, when present, was dose dependent with a half-maximal effect at 20 microM. The distal luminal membrane is the site of two Ca2+ channels with different kinetics parameters. GTPgammas increased the Vmax value of the low-affinity component exclusively, in the presence as in the absence of Na+. Finally, Ca2+ uptake by the membranes of the two segments was differently influenced by toxins: cholera toxin slightly stimulated transport by the proximal membrane, but had no influence on the distal membrane, whereas pertussis toxin decreased the cation uptake by the distal tubule membrane exclusively. We conclude that the nature of Ca2+ channels differs in the proximal and distal luminal membranes: Ca2+ channels present in the proximal tubule and the low-affinity Ca2+ channels present in the distal tubule membranes are directly regulated by Gs and Gi proteins respectively, whereas the high-affinity Ca2+ channel in the distal tubule membrane is insensitive to any of them.

Ovarian hormones modulate monocyte chemotactic protein-1 expression in endometrial cells of women with endometriosis.

Endometriosis, a frequent oestrogen-dependent disease believed to result from an aberrant proliferation of endometrial tissue outside the uterine cavity, is associated with an increased expression of monocyte chemotactic protein-1 (MCP-1) in the intrauterine endometrium. This makes it plausible that migrating endometrial cells are intrinsically able to initiate monocyte chemoattraction and activation, a phenomenon which has been consistently observed in the peritoneal cavity of patients and recently in their eutopic endometrium. To elucidate the mechanisms involved in the regulation of MCP-1 expression in eutopic endometrial cells, we studied the effects of ovarian hormones and found that oestradiol (10(-9) and 10(-8) mol/l) markedly increased MCP-1 mRNA steady-state levels and protein secretion by endometrial cells in response to interleukin-1beta (IL-1beta) (0.1 ng/ml). The IL-1beta-induced MCP-1 expression was even higher following pretreatment of cells with both oestradiol (10(-9) mol/l) and progesterone (5x10(-8) mol/l). This did not seem to be due to increased MCP-1 mRNA stability, but rather to a higher level of gene transcription. Our results provide evidence that ovarian steroids regulate, indirectly, the synthesis and the secretion of a potent chemotactic and activating factor for monocytes/macrophages by endometrial cells of women with endometriosis and reveal a new mechanism for oestradiol action.

ATP directly enhances calcium channels in the luminal membrane of the distal nephron.

Calcium (Ca(2+)) transport by the distal tubule (DT) luminal membrane is regulated by the parathyroid hormone (PTH) and calcitonin (CT) through the action of messengers, protein kinases, and ATP as the phosphate donor. In this study, we questioned whether ATP itself, when directly applied to the cytosolic surface of the membrane could influence the Ca(2+) channels previously detected in this membrane. We purified the luminal membranes of rabbit proximal (PT) and DT separately and measured Ca(2+) uptake by these vesicles loaded with ATP or the carrier. The presence of 100 microM ATP in the DT membrane vesicles significantly enhanced 0.5 mM Ca(2+) uptake from 0.57 +/- 0.02 to 0.71 +/- 0.02 pmol/microg per 10 sec (P < 0. 01) in the absence of Na(+) and from 0.36 +/- 0.03 to 0.59 +/- 0.01 pmol/microg per 10 sec (P < 0.01) in the presence of 100 mM Na(+). This effect was dose dependent with an EC(50) value of approximately 40 microM. ATP action involved the high-affinity component of Ca(2+) transport, decreasing the Km from 0.08 +/- 0.01 to 0.04 +/- 0.01 mM (P< 0.02). Replacement of the nucleotide by the nonhydrolyzable ATPgammas abolished this action. Because ATP has been reported to be necessary for cytoskeleton integrity, we also investigated the effect of intravesicular cytochalasin on Ca(2+) transport. Inclusion of 20 microM cytochalasin B decreased 0.5 mM Ca(2+) uptake from 0.33 +/- 0.01 to 0.15 +/- 0.01 pmol/microg per 10 sec (P< 0.01). However, when both 100 microM ATP and 20 microM cytochalasin were present in the vesicles, the uptake was not different from that observed with ATP alone. Neither ATP nor cytochalasin had any influence on Ca(2+) uptake by the PT luminal membrane. We conclude that the high-affinity Ca(2+) channel of the DT luminal membrane is regulated by ATP and that ATP plays a crucial role in the integrity of the cytoskeleton which is also involved in the control of Ca(2+) channels within this membrane.

Learning needs assessments: definitions, techniques, and self-perceived abilities of the hospital-based nurse educator.

The purpose of this article is to describe survey research on learning needs assessment, conducted to determine definitions, techniques, and confidence levels of the hospital-based educator. Confidence levels related to fulfillment of the needs assessment role and resources available to the nurse educator are described. In a survey of 223 hospitals, a 69% return rate showed that the hospital educator used "real need" (lack of understanding, skill, or ability) as their primary definition. Professional standards, records and reports, and technological and institutional changes were primary sources of program determination. The nurse educator was confident in traditional roles but less confident in developing competency-based evaluations and clinical simulations.

Mutation R96W in cytochrome P450c17 gene causes combined 17 alpha-hydroxylase/17-20-lyase deficiency in two French Canadian patients.

Congenital adrenal hyperplasia (CAH) is the most frequent cause of adrenal insufficiency and ambiguous genitalia in newborn children. In contrast to CAH caused by 21 alpha-hydroxylase and 11 beta-hydroxylase deficiencies, which impairs steroid formation in the adrenal exclusively, 17 alpha-hydroxylase/17,20-lyase deficiency impairs steroid biosynthesis in the adrenals and gonads. The sequence of CYP17 gene was determined by direct sequencing of asymmetric PCR products in two French-Canadian 46,XY pseudohermaphrodite siblings suffering from combined 17 alpha-hydroxylase/17,20-lyase deficiency. The two patients are homozygous for the novel missense mutation R96W caused by a C to T transition converting codon Arg96 (CGG) into a Trp (TGG) in exon 1. The both parents are heterozygous for this missense mutation. We assessed the effect of the R96W mutation on 17 alpha-hydroxylase/17,20-lyase activity by analysis of mutant enzyme, generated by site-directed mutagenesis, expressed in COS-1 cells. The presence of R96W substitution almost completely abolished the activity of the mutant protein. The present findings provide a molecular explanation for the signs and symptoms of combined 17 alpha-hydroxylase/17,20-lyase deficiency in these two patients and provide useful information on the structure-activity relationships of the P450c17, enzyme.

Kallikreins expression in a mature cystic ovarian teratoma.

We report an example of benign cystic ovarian teratoma that was incidentally discovered in a nulliparous 24-year-old woman taking contraceptive pills. Histological examination of the cyst revealed the presence of prostatelike tissue in association with a wide variety of other tissues. The use of highly specific monoclonal antibodies developed against the two prostate-specific kallikreins (hK2 and hK3) in humans allowed the demonstration that the multiple islets of epithelial cells were prostatic tissue in nature and that only part of these cells had conserved their intrinsic property of producing kallikreins.

Calcium transport by the luminal membrane of distal tubule: II. Effect of pH, electrical potential and calcium channel inhibitors.

We studied the effect of pH, electrical potential and calcium channel inhibitors on calcium (Ca2+) uptake by the luminal membranes of distal nephron from rabbit kidney. Ca2+ uptake was measured using 45Ca and the rapid filtration technique. Uptake by the luminal membranes prepared from distal tubule suspensions were compared to the corresponding values obtained with membranes from proximal tubules. In the distal tubule experiments, Ca2+ transport was measured in the presence and the absence of Na+ in the incubation medium. As previously reported, Na+ inhibited Ca2+ uptake by the distal membrane vesicles. Increasing the pH of either the extravesicular or intravesicular media, or both, enhanced Ca2+ uptake by the distal membrane vesicles. We previously described two kinetics of Ca2+ transport by the luminal membrane of the distal nephron, with high and low affinities, respectively. In both the presence and absence of Na+, alkaline pH stimulated the low affinity-high velocity system by decreasing the Km Ca2+. In the presence of Na+, alkaline pH also increased the Vmax Ca2+ of the high affinity system with no significant changes in Km. These effects of pH were not related to a H+/Ca2+ exchange mechanism. In contrast, pH did not significantly influence Ca2+ transport through the proximal membrane vesicles. When an electrical potential gradient (inside negative) across the vesicles was created by either various anion gradients through the membranes, or by inducing K+ efflux with valinomycin, no relation could be detected between the electrical gradient and 0.5 mM Ca2+ uptake by the proximal or distal membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium transport through the luminal membrane of the distal tubule. I. Interrelationship with sodium.

Calcium (Ca2+) transport by isolated luminal membranes from rabbit renal distal tubule has been characterized. Ca2+ uptake by these membrane vesicles exhibited saturation kinetics. In the absence of sodium (Na+) in the incubation medium, a low affinity system was observed with a KmCa2+ of 2.83 +/- 0.64 mM and Vmax of 3.03 +/- 0.48 pmol/microgram/10 sec. A second type of kinetics was also detected with a high affinity and a low velocity (KmCa2+ 0.04 +/- 0.01 mM, Vmax 1.18 +/- 0.22 pmol/micrograms/10 sec). The luminal membranes from proximal tubules showed a single system with a KmCa2+ of 0.49 +/- 0.20 mM and Vmax of 1.26 +/- 0.17 pmol/micrograms/10 sec. The presence of Na+ sharply decreased Ca2+ uptake by the high affinity system of the membranes from distal tubules, increasing the KmCa2+ to 0.07 mM +/- 0.01 (P less than 0.01) and decreasing the Vmax to 0.27 pmol/microgram/10 sec (P less than 0.005). This effect of Na+ was concentration-dependent, with a half-maximal effect at 38 mM Na+ and a Hill coefficient of 0.9. In contrast, Na+ had no effect on Ca2+ transport through the luminal membranes of proximal tubules nor on the low affinity system of the distal tubule. The composition of the intravascular medium also influenced Ca2+ uptake by the membranes from distal tubules. Compared to mannitol, trans-Na+ or K+ significantly reduced Ca2+ transport. Finally, cis-K+ induced an increase in this transport. As found with Na+, the effect of K+ was concentration-dependent, with a Hill coefficient of 0.42.(ABSTRACT TRUNCATED AT 250 WORDS)