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There is increasing interest in the role of calcium in a variety of biological processes. One of the mechanisms that regulate intracellular calcium concentrations is the calcium-activated adenosine triphosphatases (Ca2+-ATPase). The availability of an histochemical method for ultrastructural localization of Ca2+-ATPase has led to a number of studies attempting to localize this enzyme in a variety of cell types. This ultrastructural study was undertaken to localize Ca2+-ATPase in walls of intracerebral cortical vessels of rats. Both capillary and arteriolar endothelium showed discontinuous deposits of Ca2+-ATPase along the outer plasma membrane including the junctional plasma membranes. Patchy distribution of Ca2+-ATPase was also observed on the outer plasma membranes of smooth muscle and adventitial cells. Focal deposits of reaction product were associated with the actin filaments in endothelium. Invaginating pinocytotic vesicles at the outer plasma membrane of endothelium and smooth muscle cells showed Ca2+-ATPase. Intracytoplasmic vesicles showed the enzyme along the inner plasma membrane. Localization of Ca2+-ATPase on endothelial plasma membranes suggests that Ca2+ may be involved in many endothelial reactions. Further studies are required to determine the role of this enzyme and Ca2+ in endothelial reactions in normal and abnormal states.
The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-5.4 x 10(-4) M) on microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent adenosine triphosphatase (ATPase) activities was studied in vitro. Adrenochrome decreased microsomal calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The inhibitory effect of adrenochrome on microsomal calcium uptake activity of the isolated membrane was independent of pH (6.0-8.0), calcium concentrations (10-200 muM), protein concentration (0.02-0.10 mg/ml), temperature (25-37 degrees C) and incubation time (2-30 min). Kinetic study of calcium uptake activity in different concentrations of ATP showed that the inhibition was of a mixed type. Perfusion of hearts with adrenochrome resulted in marked depression in contractile force and the microsomal fraction obtained from these hearts showed depressed calcium binding, calcium uptake and Ca++-stimulated Mg++-dependent ATPase activities. The depression in microsomal The influence of adrenochrome (1-100 microgram/ml or 5.6 x 10(-6)-an irreversible nature. It is proposed that cardiodepressant action of adrenochrome may partly be explained on the basis of its inhibitory effect on the calcium transporting ability of the sarcoplasmic reticulum.
BACKGROUND: The mechanisms of intestinal adaptation after resection are not completely defined. The purpose of this study was to examine the changes after resection in the enterocyte basolateral Na+,K+ adenosine triphosphatase (ATPase) known to play a critical role in epithelial transport and homeostasis. METHODS: Lewis rats underwent 70% small bowel resection or transection. At 6 hours, 24 hours, 1 week, and 2 weeks, jejunum and ileum were harvested for analysis of Na+,K+ ATPase activity, kinetic analysis, and alpha 1-ATPase messenger RNA and protein levels. RESULTS: Na+,K+ ATPase activity increased (p < 0.05) in both the jejunum and ileum by 2 weeks after resection. This rise in activity correlated with an increase in the maximal activity of ATPase, from 20.8 to 101.01 mumol inorganic phosphate.mg-1.hr-1. ATPase messenger RNA levels increased sixfold in the jejunum and tenfold in the ileum by 2 weeks after resection (p < 0.05). Protein levels rose at 6 hours and remained elevated in both tissues. CONCLUSIONS: After intestinal resection, enterocyte Na+,K+ ATPase activity rises as a result of an increase in the number of transporters per cell. This occurs through both transcriptional and translational mechanisms. It appears that intestinal adaptation after resection involves not only an increase in absorptive surface area but also functional adaptation by the individual enterocyte.
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The effect of culture conditions, serum supplementation or chemically defined medium and the influence of thyroid hormone were studied on the development of the Na+, K+-adenosine triphosphatase (Na+,K+-ATPase) and on the intracellular content of K+ and Na+ ions in cultures which either were greatly enriched in a neuronal cell type, the cerebellar granule cells, or contained a mixed population of cells (brain reaggregates). Foetal rat brain reaggregates displayed lower Na+,K+-ATPase activity when cultured in chemically defined medium than in the presence of serum. Supplementation of the serum-free medium with thyroid hormone resulted in a rise in the Na+,K+-ATPase activity and [3H]ouabain binding to levels similar to those found in the cultures grown in the serum-containing medium. Thyroid hormone had no significant effect on the Mg2+-ATPase activity and on the intracellular content of Na+ and K+ ions. In the granule cell-enriched cerebellar surface cultures the Na+,K+-ATPase activity was lower when the cells were grown in chemically defined medium compared with the serum-containing medium, and the intracellular Na+ to K+ ratio was higher. Thyroid hormone had no effect on the Na+,K+-ATPase activity, [3H]ouabain binding or Mg2+-ATPase activity. The hormone also failed to influence ATPase activities in cerebellar astrocytes maintained in chemically defined medium. Although thyroid hormone had no effect on the Na+,K+-ATPase activity of cultured cerebellar granule cells, treatment with the hormone resulted in a decrease in the ratio of intracellular Na+ to K+ ion content. The effect of the hormone on the Na+,K+-pump activity in live cells was therefore tested by estimating ouabain-sensitive 86Rb uptake. This was regulated as in other cell types, by the rate of Na+ entry: the Na+-ionophore monensin trebled the rate of 86Rb uptake, which was also increased (+30-100%) by 10% foetal calf serum, the maximal response being obtained by about 20 min exposure to serum. The effect was completely blocked by the Na+/H+ exchange inhibitor amiloride. The factor(s) in the serum responsible for the regulation of the Na+,K+-pump were, however, not the thyroid hormones, which failed to affect 86Rb uptake. On the basis of comparing thyroid hormone effects on the different cultures studied it was concluded that not every type of neural cell is target of the hormone action during development.
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The cerium-based method was used to demonstrate cytochemically the ultrastructural localization of alkaline phosphatase (ALPase), 5'-nucleotidase (5'-Nase) and magnesium-dependent adenosine triphosphatase (Mg-ATPase) on the transitional epithelium of the rat urinary bladder. The reaction product for ALPase was found on the plasma membrane of all epithelial cells, except the luminal surface of superficial cells. The activity of 5'-Nase appeared on the plasma membrane of all bladder transitional epithelial cells, including the free surface of superficial cells. The Mg-ATPase reaction product was seen on the plasma membrane of superficial, intermediate and basal cells, but never on the luminal surface of superficial cells and it was only occasionally seen on the basal surface. The possible functions of these phosphatases have been discussed, and it was emphasized that the 5'-Nase activity present on the luminal surface of superficial cells may play a special role in the membrane movement of these cells in the transitional epithelium.
A pathogenic role and abnormal function have both been ascribed to the blood platelet in allergy, but the explanation for these observations is unknown. This study compared the cation-stimulated adenosine triphosphatase enzyme (ATPase) activities of platelets from allergic (n = 18), potentially allergic (asymptomatic, positive skin test, n = 5) and normal patients (n = 10), all of whom were without symptoms at the time of the study. Platelets were separated by centrifugation, were sonicated, and were assayed for cation-dependent ATPase activity by spectrophotometry. The mean Na+,K(+)-ATPase activity (in nanomoles per microgram protein per minute) of allergic subjects (0.94 +/- 1.28) was significantly lower than that of normal subjects (3.93 +/- 1.58). No Na+,K(+)-ATPase activity was detectable in platelets from eight of the allergic subjects. The Na+,K(+)-ATPase activity of potentially allergic subjects was intermediate between those of the allergic and normal subjects. A significant negative correlation (p less than 0.01) was observed between serum IgE levels and platelet Na+,K(+)-ATPase values, thus suggesting a relationship between the reduced platelet Na+,K(+)-ATPase and IgE immunoglobulin. No such differences were observed for the Ca+(+)- and Mg+(+)-stimulated ATPases. In vivo dysfunction of the plasma membrane Na+,K(+)-ATPase enzyme in allergic subjects could have profound effects on levels of intracellular cations and thus platelet activation and function.
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