Seasonal composition, abundance and biomass of the subestuarine fish assemblage in Solís Chico (Río de la Plata estuary, Uruguay) / Composição, abundância e biomasa sazonal da assembleia de peixes no subestuário do Solís Chico (Estuário do Río de la Plata, Uruguay)

Abstract The large estuaries can present long narrow branches called subestuaries or tidal creeks. These types of subsystems are distributed along the Uruguayan coast of the Río de la Plata estuary and are very important as nursery and refuge areas for fish. For the first time, the seasonal composition and abundance of the fish community of the Solís Chico subestuary was studied by using beach and gill nets. Fourteen species, mainly euryhaline (86%) presented a significant representation of juvenile stages. The fish community was dominated by Odontesthes argentinensis, Platanichthys platana, Mugil liza, Brevoortia aurea, Micropogonias furnieri and Paralichthys orbignyanus, similar to adjacent subestuaries. While Micropogonias furnieri and B. aurea were the most abundant species, some other species were rarely caught. A seasonal variation of the fish assemblage abundance was detected, with higher values in autumn showing a positive correlation with temperature. Species that complete their life cycle in the Río de la Plata estuary, some of which are relevant to fisheries (64% of the analyzed species) were captured in the Solís Chico subestuary. The importance of this environment as a transitional system for some estuarine fish species is advised.

Resumo Os grandes estuários podem apresentar longos ramos estreitos chamados subestuários e riachos de maré. Estes subsistemas estão distribuídos ao longo da costa uruguaia no estuário do Río de la Plata e são muito importantes como áreas de reprodução e refúgio para os peixes. Pela primeira vez, a composição sazonal e abundância da comunidade de peixes do subestuário Solís Chico foi estudada usando redes de arrasto de praia e rede de emalhar. Quatorze espécies com predominância das eurialinas foram capturadas, havendo uma representação significativa das fases juvenis e espécies alvo para a pesca. A comunidade de peixes foi dominada por Odontesthes argentinensis, Platanichthys platana, Mugil liza, Brevoortia aurea, Micropogonias furnieri e Paralichthys orbignyanus, semelhante aos subestuários adjacentes. Enquanto, M. furnieri e B. aurea foram as espécies com maior número de individuos. Solís Chico apresentou espécies exclusivas com baixa abundância e ocorrência. Foi verificada uma variação sazonal da abundância de peixes, com valores maiores no outono, mostrando uma correlação positiva com a temperatura. Algumas espécies relevantes para a pesca que completam seu ciclo de vida no estuário do Río de la Plata foram capturadas (64% das espécies estudadas) no subestuário Solís Chico, indicando a importância deste ambiente como um sistema transitório para algumas espécies estuarinas de peixes.

Gender ratio trends over time in multiple sclerosis patients from Argentina.

Several studies in multiple sclerosis (MS) suggest a trend of increasing disease frequency in women during the last decades. A direct comparison of gender ratio trends among MS populations from Argentina remains to be carried out. The objective of the study was to compare gender ratio trends, over a 50-year span in MS populations from Argentina. METHODS: multicenter study that included patients from 14 MS Centers of Argentina. Patients with definite MS with birth years ranging from 1940 to 1989 were included. Gender ratios were calculated by five decades based on year of birth and were adjusted for the F/M born-alive ratio derived from the Argentinean national registry of births. The F/M ratios were calculated using a multivariate logistic regression per five decades by the year of birth approach. Analyses were performed using Stata 10.1. RESULTS: 1069 patients were included. Gender ratios showed a significant increase from the first to the last decade in the whole MS sample (from 1.8 to 2.7; p value for trend=0.023). The Gender ratio did not show differences considering MS subtype. CONCLUSION: our study showed a modest increase of the F/M ratio (from 1.8 to 2.7) over time among patients affected by MS in Argentina.

Seasonal composition, abundance and biomass of the subestuarine fish assemblage in Solís Chico (Río de la Plata estuary, Uruguay).

The large estuaries can present long narrow branches called subestuaries or tidal creeks. These types of subsystems are distributed along the Uruguayan coast of the Río de la Plata estuary and are very important as nursery and refuge areas for fish. For the first time, the seasonal composition and abundance of the fish community of the Solís Chico subestuary was studied by using beach and gill nets. Fourteen species, mainly euryhaline (86%) presented a significant representation of juvenile stages. The fish community was dominated by Odontesthes argentinensis, Platanichthys platana, Mugil liza, Brevoortia aurea, Micropogonias furnieri and Paralichthys orbignyanus, similar to adjacent subestuaries. While Micropogonias furnieri and B. aurea were the most abundant species, some other species were rarely caught. A seasonal variation of the fish assemblage abundance was detected, with higher values in autumn showing a positive correlation with temperature. Species that complete their life cycle in the Río de la Plata estuary, some of which are relevant to fisheries (64% of the analyzed species) were captured in the Solís Chico subestuary. The importance of this environment as a transitional system for some estuarine fish species is advised.

Disease onset in familial and sporadic multiple sclerosis in Argentina.

UNLABELLED: The present study was carried out to assess if there is an anticipation of age at onset in younger generations of familial multiple sclerosis (FMS) vs. sporadic MS (SMS) in Argentina. METHODS: multicenter study that included patients from 14 MS Centers of Argentina. Patients were considered as FMS if they had in their family at least one relative of first or second degree diagnosed with MS; otherwise, patients were considered to have SMS. We compared the age at onset between familial and sporadic cases as well as the age at onset between relatives from different generations in FMS vs. SMS. RESULTS: 1333 patients were included, 97 of them were FMS (7.3%). A lower age at onset in the younger generations of FMS cases was found compared with older generations of FMS as well as. SMS cases (24.1±3.7 years vs. 30.3±5.7 years, and 32.4±9.4 respectively; p<0.001). No differences were observed between older generations of FMS vs. SMS cases (p=0.12). CONCLUSION: we observed an anticipation of age at onset of MS in younger generations of patients with FMS vs. older generations of FMS and SMS.

Cadmium effects on 24h changes in glutamate, aspartate, glutamine, GABA and taurine content of rat striatum.

This work evaluates the possible changes in 24 h variations of striatal aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine content after oral cadmium treatment. Male rats were submitted to cadmium exposure at two doses (25 and 50 mg/L of cadmium chloride (CdCl(2))) in the drinking water for 30 days. Control rats received cadmium-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. Differential effects of cadmium on 24 h amino acid fluctuations were observed. Metal exposure modified the daily pattern of the amino acids concentration found in control animals, except for GABA and taurine with the lowest dose used. Exposure to 25 mg/L of CdCl(2) decreased mean content of aspartate, as well as GABA concentration. These results suggest that cadmium exposure affects 24 h changes of the studied amino acids concentration in the striatum, and those changes may be related to alterations in striatal function.

Endosulfan effects on pituitary hormone and both nitrosative and oxidative stress in pubertal male rats.

The present study was undertaken to investigate in pubertal male rats possible effects of endosulfan administered throughout lactation and gestation on: (a) pituitary gene expression of prolactin, luteinizing hormone (LH), growth hormone (GH) and thyroid stimulating hormone (TSH); (b) circulating levels of these hormones; and (c) expression of nitric oxide synthase 1 and 2 (NOS1 and NOS2), and heme oxygenase-1 (HO-1) at pituitary level. Endosulfan was administered orally at the doses of 0.61 mg/kg/day or 6.12 mg/kg/day, and possible toxic effects were studied in pubertal male pups (at postnatal day 30). Gene expression was evaluated by RT-PCR and plasma hormone levels by RIA. Exposure to both administered doses down-regulated LH, GH and TSH. Treatment with 0.61 mg endosulfan/kg/day decreased prolactin expression, although its plasmatic concentration was decreased by both administered doses. LH secretion was stimulated by both doses, whereas the highest dose increased GH levels and decreased plasma TSH concentration. Endosulfan up-regulated NOS1 and NOS2. We can conclude that in pubertal male rat, prenatal and lactational exposure to endosulfan modifies expression and release of prolactin, LH, GH and TSH, and pituitary NOS1 and NOS2 mRNA levels, suggesting that nitrosative stress can be implicated in the endocrine toxicity of endosulfan at pituitary level.

Cadmium chloride exposure modifies amino acid daily pattern in the mediobasal hypothalamus in adult male rat.

The present study was conducted to investigate the possible effects of cadmium exposure on the daily pattern of aspartate, glutamate, glutamine, gamma-aminobutyric acid (GABA) and taurine levels in the mediobasal hypothalamus of adult male rats. For this purpose, animals were treated with cadmium at two different exposure doses (25 and 50 mg l(-1) of cadmium chloride, CdCl(2)) in the drinking water for 30 days. Control age-matched rats received CdCl(2)-free water. After the treatment, rats were killed at six different time intervals throughout a 24 h cycle. CdCl(2) exposure modified the amino acid daily pattern, as it decreased aspartate, glutamate, GABA and taurine levels at 12:00 h with both exposure doses employed. In addition, the treatment with 25 mg l(-1) of CdCl(2) induced the appearance of minimal values at 16:00 h and maximal values between 04:00 and 08:00 h for glutamate, and a peak of glutamine content at 20:00 h. The heavy metal also decreased GABA medium levels around the clock in the mediobasal hypothalamus. However, CdCl(2) did not alter the metabolic correlation between glutamate, aspartate, glutamine and GABA observed in control animals. These results suggest that CdCl(2) induced several alterations in aspartate, glutamate, glutamine, GABA and taurine daily pattern in the mediobasal hypothalamus and those changes may be related to alterations in hypothalamic function.

Cadmium exposure disrupts GABA and taurine regulation of prolactin secretion in adult male rats.

This work was undertaken to evaluate the possible effects of cadmium exposure on 24 h changes of gamma-aminobutyric acid (GABA) and taurine median eminence and pituitary contents. Also the possible alterations of the regulatory mechanisms of GABA and taurine on prolactin secretion were evaluated. Adult male rats were given cadmium at a dose of 25 mg/l of cadmium chloride in the drinking water for 30 days. Control age-matched rats received cadmium free water. Metal exposure induced the appearance of a maximal value of prolactin at 08:00 h. In median eminence, cadmium abolished the GABA and taurine maximal values and decreased GABA and taurine mean levels. In the anterior pituitary, cadmium treatment phase advanced 12 h the peak observed in controls at 00:00 h for both amino acids. There was a positive correlation between GABA and taurine contents in median eminence and the anterior pituitary in both control and cadmium-exposed animals. However, the correlation between GABA or/and taurine with prolactin levels disappeared in cadmium-exposed animals. These results suggest that cadmium exposure affects GABA and taurine daily pattern in the median eminence and anterior pituitary, and those changes explain, at least in part, the modification in the regulatory pattern of prolactin secretion.

Toxic effects of methoxychlor administered subcutaneously on the hypothalamic-pituitary-testicular axis in adult rats.

This study was undertaken to evaluate the effects of methoxychlor MTX at the hypothalamic-pituitary-testicular axis in adult male rats. This global objective comprises three major aims: (1) to analyze the possible differential MTX effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence; (2) to evaluate effects induced by MTX exposure on gonadotropins and testosterone; 93 to elucidate whether the regulatory interactions in the hypothalamic-pituitary-testicular axis are modified by this pesticide. Animals were administered subcutaneously 25mg/kg/day of MTX for 1 month. MTX increased norepinephrine and serotonin content in anterior hypothalamus (P < or = 0.05), but decreased serotonin concentration in posterior hypothalamus (P < or = 0.05). MTX diminished serotonin turnover in anterior hypothalamus (P < or = 0.01) and decreased plasma LH (P < or = 0.001) and testosterone (P < or = 0.05) levels but those of FSH remained unmodified. We can conclude that MTX exposure: (1) could exert differential effects in norepinephrine and serotonin concentration an in serotoninergic metabolism in anterior, mediobasal and posterior hypothalamus and median eminence, being the anterior hypothalamus the most sensitive region to the pesticide; (2) could inhibit LH and testosterone secretion without changing FSH; (3) four potential pathways might be involved in MTX effects on testosterone secretion (changing LH secretion; modifying serotonin and norepinephrine at the hypothalamic level; alterating the direct neural pathway between brain and testes; and/or by a direct effect in testes).

Posible papel protector de la melatonina frente a la toxicidad neuroendocrina inducida por cadmio / Possible protective role of melatonin in the neuroendocrine toxicity induced by cadmium

El cadmio es un agente químico tóxico importante debido a su creciente nivel en el medio ambiente como resultado de prácticas industriales y agrícolas. Como perturbador endocrino, el cadmio modifica la secreción de hormonas hipofisarias. Los efectos indirectos del cadmio provocan la generación de especies reactivas de oxígeno y reducen la actividad de las proteínas implicadas en las defensas antioxidantes. La melatonina es conocida como un potente antioxidante, scavenger de radicales libres y quelante de metales sintetizada en la glándula pineal. De esta manera, las acciones antioxidantes de esta indolamina protegen frente a la peroxidación lipídica y el daño oxidativo de los radicales y de sus productos tóxicos. Los trabajos recopilados en esta revisión ponen de manifiesto la capacidad antioxidante de la melatonina y, por lo tanto, su posible papel protector frente a la toxicidad del cadmio en lo que se refiere al estrés oxidativo y peroxidación lipídica inducidos por la exposición a este metal (AU)

Cadmium is one of the most important toxic chemicals due to its increasing level in the environmentas a result of industrial and agricultural practices. As an endocrine disruptor, cadmium modifies pituitary hormone release. Indirect effects of cadmium provoke generation of reactive oxygen species and reduce activities of proteins involved in antioxidant defenses. Melatonin is a well-known potent antioxidant, free radical scavenger and metal chelator synthesized in the pineal gland. Thus, antioxidative actions of this nature protect against lipid peroxidation and oxidative damage by radicals and their toxic products. This review collates evidence from many research laboratories who reported antioxidant effects of melatonin and this mechanism could counteract oxidative stress and lipid peroxidation induced by cadmium exposure (AU)

Plasma-membrane Ca(2+) pumps: structural diversity as the basis for functional versatility.

Plasma-membrane calcium pumps [PMCAs (plasma-membrane Ca(2+)-ATPases)] expel Ca(2+) from eukaryotic cells to maintain overall Ca(2+) homoeostasis and to provide local control of intracellular Ca(2+) signalling. Recent work indicates functional versatility among PMCA isoforms, with specific pumps being essential for cochlear hair cell function, sperm motility, feedback signalling in the heart and pre- and post-synaptic Ca(2+) regulation in neurons. The functional versatility of PMCAs is due to differences in their regulation by CaM (calmodulin), kinases and other signalling proteins, as well as to their differential targeting and retention in defined plasma membrane domains. The basis for this is the structural diversity of PMCAs. In mammals, four genes encode PMCA isoforms 1-4, and each of these has multiple variants generated by alternative RNA splicing. The alternatively spliced regions are intimately involved in the regulatory interactions and differential membrane localization of the pumps. The alternatively spliced C-terminal tail acts as an autoinhibitory domain by interacting with the catalytic core of the pump. The degree of inhibition and the kinetics of interaction with the major activator CaM differ between PMCA variants. This translates into functional differences in how PMCAs handle Ca(2+) signals of different magnitude and frequency. Accumulating evidence thus demonstrates how structural diversity provides functional versatility in the PMCAs.

Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters.

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present. This study was undertaken to evaluate the possible effects of MTX in norepinephrine, dopamine and amino acid contents and serotonin turnover in rat striatum. For this purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day of MTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interest were measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However, the content of serotonin, aspartate, glutamine and taurine was not modified by MTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesis and serotonin metabolism. The inhibitory effect on norepinephrine could be explained, at least in part, by the increase of both GABA and glutamate contents. Further studies are needed to understand the effects of MTX on serotonin. Also a disruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine and GABA emerges.

Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present.This study was undertaken to evaluate the possible effects of MTX in norepinephrine,dopamine and amino acid contents and serotonin turnover in rat striatum. Forthis purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day ofMTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interestwere measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However,the content of serotonin, aspartate, glutamine and taurine was not modified byMTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesisand serotonin metabolism. The inhibitory effect on norepinephrine could beexplained, at least in part, by the increase of both GABA and glutamate contents.Further studies are needed to understand the effects of MTX on serotonin. Also adisruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine andGABA emerges (AU)

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Toxic effects of methoxychlor in rat striatum: modifications in several neurotransmitters

Neurotoxic effects of methoxychlor (MTX) are poorly understood at present.This study was undertaken to evaluate the possible effects of MTX in norepinephrine,dopamine and amino acid contents and serotonin turnover in rat striatum. Forthis purpose, adult male Sprague-Dawley rats were administered 25 mg/kg/day ofMTX in sesame oil or vehicle only for 30 days. The neurotransmitters of interestwere measured in the striatum by HPLC. MTX decreased norepinephrine and 5-hydroxyindole acetic acid (5-HIAA) content and serotonin turnover (measured as 5-HIAA/serotonin ratio), and increased glutamate and GABA concentrations. However,the content of serotonin, aspartate, glutamine and taurine was not modified byMTX exposure. These data suggest that MTX exposure inhibits norepinephrine synthesisand serotonin metabolism. The inhibitory effect on norepinephrine could beexplained, at least in part, by the increase of both GABA and glutamate contents.Further studies are needed to understand the effects of MTX on serotonin. Also adisruptive effect of MTX on the metabolisms of glutamate, aspartate, glutamine andGABA emerges (AU)

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Expression and cellular distribution pattern of plasma membrane calcium pump isoforms in rat pancreatic islets.

This work is aimed at identifying the presence and cellular distribution pattern of plasma membrane calcium pump (PMCA) isoforms in normal rat pancreatic islet. Microsomal fractions of isolated islets and exocrine tissue were analyzed to detect different PMCA isoforms. The cellular distribution pattern of these PMCAs in the islets was also studied in fixed pancreas sections incubated with antibodies against PMCAs and insulin. Antibody 5F10, which reacts with all PMCA variants, showed multiple bands in the blots in the 127-134 kDa region, indicating the presence of several isoforms. Microsomes also reacted positively with specific antibodies for individual PMCA isoforms, generating a band of the expected size. Antibody 5F10 immunocytochemically labeled the plasma cell membrane of both b- and non-b-cells, but predominantly the former. All islet cells were also labeled with antibodies against isoforms 1 and 4, while the antibody reacting with isoform 3 labeled exclusively b-cells. A few b- and non-b-cells were positively labeled with the antibody reacting with PMCA b variant. Negative results were obtained with the antibody against isoform 2. Further studies, together with previous reports on the modulatory effect of insulin secretagogues and blockers upon PMCA activity, may provide evidence of the importance of this particular PMCA expression for islet function under normal and pathological conditions.

The plasma membrane calcium pump displays memory of past calcium spikes. Differences between isoforms 2b and 4b.

To understand how the plasma membrane Ca(2+) pump (PMCA) behaves under changing Ca(2+) concentrations, it is necessary to obtain information about the Ca(2+) dependence of the rate constants for calmodulin activation (k(act)) and for inactivation by calmodulin removal (k(inact)). Here we studied these constants for isoforms 2b and 4b. We measured the ATPase activity of these isoforms expressed in Sf9 cells. For both PMCA4b and 2b, k(act) increased with Ca(2+) along a sigmoidal curve. At all Ca(2+) concentrations, 2b showed a faster reaction with calmodulin than 4b but a slower off rate. On the basis of the measured rate constants, we simulated mathematically the behavior of these pumps upon repetitive changes in Ca(2+) concentration and also tested these simulations experimentally; PMCA was activated by 500 nm Ca(2+) and then exposed to 50 nm Ca(2+) for 10 to 150 s, and then Ca(2+) was increased again to 500 nm. During the second exposure to 500 nm Ca(2+), the activity reached steady state faster than during the first exposure at 500 nm Ca(2+). This memory effect is longer for PMCA2b than for 4b. In a separate experiment, a calmodulin-binding peptide from myosin light chain kinase, which has no direct interaction with the pump, was added during the second exposure to 500 nm Ca(2+). The peptide inhibited the activity of PMCA2b when the exposure to 50 nm Ca(2+) was 150 s but had little or no effect when this exposure was only 15 s. This suggests that the memory effect is due to calmodulin remaining bound to the enzyme during the period at low Ca(2+). The memory effect observed in PMCA2b and 4b will allow cells expressing either of them to remove Ca(2+) more quickly in subsequent spikes after an initial activating spike.

Delayed activation of the plasma membrane calcium pump by a sudden increase in Ca2+: fast pumps reside in fast cells.

There are four genes encoding isoforms of the plasma membrane Ca(2+) pump (PMCA). PMCA variability is increased by the presence of two splicing sites. Functional differences between the variants of PMCA have been described, but little is known about the adaptive advantages of this great diversity of pumps. In this paper we studied how the different isoforms respond to a sudden increase in Ca(2+) concentration. We found that different PMCAs are activated by Ca(2+) at different rates, PMCA 3f and 2a being the fastest, and 4b the slowest. The rate of activation by Ca(2+) depends both on the rate of calmodulin binding and the magnitude of the activation by calmodulin. We found that 2a is located in heart and the stereocilia of inner ear hair cells, 3f in skeletal muscle and 4b was identified in Jurkat cells. Both cardiac and skeletal muscle, and stereocilia recover very rapidly after a cytoplasmic Ca(2+)peak, while in Jurkat cells the recovery takes up to a minute. In stereocilia, 2a is the only method for export of Ca(2+), making the analysis of them unusually straightforward. This indicates that these rates of PMCA activation by Ca(2+) are correlated with the speed of Ca(2+) concentration decay after a Ca2 spike in the cells in which these variants of PMCA are expressed. The results suggest that the type of PMCA expressed will correspond with the speed of Ca(2+) signals in the cell.

Chimaeras reveal the role of the catalytic core in the activation of the plasma membrane Ca2+ pump.

Isoform 2b of the plasma membrane calcium pump differs from the ubiquitous isoform 4b in the following: (a) higher basal activity in the absence of calmodulin; (b) higher affinity for calmodulin; and (c) higher affinity for Ca(2+) in the presence of calmodulin [Elwess, Filoteo, Enyedi and Penniston (1997) J. Biol. Chem. 272, 17981-17986]. To investigate which parts of the molecule determine these kinetic differences, we made four chimaeric constructs in which portions of isoform 2b were grafted into isoform 4b: chimaera I contains only the C-terminal regulatory region of isoform 2b; chimaera II contains the N-terminal moiety of isoform 2b, including both cytoplasmic loops; chimaera III contains the sequence of isoform 2b starting from the N-terminus to after the end of the first (small) cytoplasmic loop; and chimaera IV contains only the second (large) cytoplasmic loop. Surprisingly, chimaera I showed low basal activity in the absence of calmodulin and low affinity for calmodulin, unlike isoform 2b. In contrast, the chimaera containing both loops showed high basal activity, and Ca(2+) activation curves (both in the absence and in the presence of calmodulin) similar to those of isoform 2b. The rates of activation by calmodulin and of inactivation by calmodulin removal were measured, and the apparent K(d) for calmodulin was calculated from the ratio between these rate constants. The order of affinity was: 2b=II>4b=IV>III=I. From these results it is clear that the construct that most closely resembles isoform 2b is chimaera II. This shows that, in order to obtain an enzyme with properties similar to those of isoform 2b, both cytoplasmic loops are needed.

Selective decrease of mRNAs encoding plasma membrane calcium pump isoforms 2 and 3 in rat kidney.

BACKGROUND: Although the existence of multiple isoforms of plasma membrane calcium ATPase (PMCA) is now well documented, their biological functions are not yet known. In this study, we set out to investigate the potential role of PMCA isoforms, previously identified in renal cortical tissue, in tubular reabsorption of calcium (Ca2+). METHODS: With use of reverse transcription-polymerase chain reaction analysis, we determined levels of mRNAs encoding isoforms of PMCA1 through PMCA4 in renal cortex, liver, and brain of rats with hypercalciuria induced by feeding with a low-phosphate diet (LPD) as compared with Ca2+-retaining rats that were fed a high-phosphate diet (HPD). RESULTS: We observed that in hypercalciuric LPD-fed rats, the mRNAs encoding isoforms PMCA2b and PMCA3(a + c) are significantly lower (Delta approximately-50%) than in HPD-fed hypocalciuric rats, whereas no changes in mRNAs encoding isoforms PMCA1b and PMCA4 were observed, and mRNA encoding calbindin 28 kDa was increased. On the other hand, the content of mRNAs encoding PMCA2b and PMCA3(a + c) in liver and brain, respectively, was not changed. CONCLUSION: These findings are evidence that expression of PMCA isoforms in the kidney can be selectively modulated in response to pathophysiologic stimuli. The association of a decrease in mRNA encoding PMCA2b and PMCA3(a + c) with hypercalciuria suggests that the two PMCA isoforms may be operant in tubular reabsorption of Ca2+ and its regulation.

The rate of activation by calmodulin of isoform 4 of the plasma membrane Ca(2+) pump is slow and is changed by alternative splicing.

A reconstitution system allowed us to measure the ATPase activity of specific isoforms of the plasma membrane Ca(2+) pump continuously, and to measure the effects of adding or removing calmodulin. The rate of activation by calmodulin of isoform 4b was found to be very slow, with a half-time (at 235 nM calmodulin and 0.5 microM free Ca(2+)) of about 1 min. The rate of inactivation of isoform 4b when calmodulin was removed was even slower, with a half-time of about 20 min. Isoform 4a has a lower apparent affinity for calmodulin than 4b, but its activation rate was surprisingly faster (half time about 20 s). This was coupled with a much faster inactivation rate, consistent with its low affinity. A truncated mutant of isoform 4b also had a more rapid activation rate, indicating that the downstream inhibitory region of full-length 4b contributed to its slow activation. The results indicate that the slow activation is due to occlusion of the calmodulin-binding domain of 4b, caused by its strong interaction with the catalytic core. Since the activation of 4b occurs on a time scale comparable to that of many Ca(2+) spikes, this phenomenon is important to the function of the pump in living cells. The slow response of 4b indicates that this isoform may be the appropriate one for cells which respond slowly to Ca(2+) signals.