The influence of aging on parathyroid hormone-induced enhancement in (Ca2+ + Mg2+)-ATPase activity of rabbit renal basolateral membrane]

We studied the influence of aging on the stimulatory effect of parathyroid hormone (PTH) to (Ca2+ + Mg2+)-ATPase activity of rabbit renal basolateral membrane (BLM). Stimulated by PTH, (Ca2+ + Mg2+)-ATPase activity of BLM from aged rabbits was lower than those from young rabbits. However, the stimulatory effect of cyclic AMP (cAMP) showed no differences in terms of (Ca2+ + Mg2+)-ATPase activity in BLM from aged and young rabbits. As cAMP production in BLM caused by PTH stimulation was not measured, it is unclear whether cAMP production is different in BLM from young and aged rabbits. From these results, we concluded that in BLM from aged rabbit, the lower effect of PTH on (Ca2+ + Mg2+)-ATPase is due to lower production of cAMP or some other disorder of the PTH signal transduction mechanism. As (Ca2+ + Mg2+)-pump plays an important role in Ca2+ reabsorption in kidney, its lower activity in aged rabbit may be one reason for aberration of renal calcium handling.     

Hormonal regulation of (Ca2+ + Mg2+)ATPase activity in canine renal basolateral membrane

High affinity (Ca2+ + Mg2+)ATPase activity was demonstrated in proximal tubule basolateral membranes (BLM) obtained from canine kidney. The Km of the enzyme for free Ca2+ was 0.12 +/- 0.02 microM, and at 3 microM free Ca2+, the enzyme reached its maximal velocity. To evaluate hormonal regulation of this enzyme, we studied the in vitro effects of several polypeptide hormones on enzyme activity. We measured the effects of insulin and human (h) PTH-(1-34) and their inactive analogs desoctapeptide insulin, bovine (b) PTH-(3-34), and oxidized hPTH-(1-34); insulin-like growth factors (IGFs) I and II; calcitonin; and the common cellular mediator for PTH and calcitonin, cAMP. At 0.1 microM free Ca2+, insulin (25-100 microU/ml) increased (Ca2+ + Mg2+)ATPase activity in a dose-dependent manner by 35-52% (P less than 0.01) and by 8-13% (P less than 0.05 to P less than 0.01) at a 3-microM free Ca2+ concentration; hPTH-(1-34) PTH (10(-9)-10(-7) M) increased the enzyme activity at a free Ca2+ concentration of 0.1 microM by 13-25% (P less than 0.05 to P less than 0.01). IGF-I increased (Ca2+ + Mg2+)ATPase activity by 40% (P less than 0.05) at 0.1 microM free Ca2+ at high peptide concentrations (10 ng/ml). No effect was obtained at 2 ng/ml IGF-I. cAMP (10(-7)-10(-4) M) stimulated enzyme activity by 18-27% (P less than 0.05 to P less than 0.02) at 0.1 microM Ca2+ and by 8-12% (P less than 0.05 to P less than 0.01) at 3 microM Ca2+. The effects of insulin and cAMP on (Ca2+ + Mg2+)ATPase activity were additive. No effect on the enzyme activity was obtained by the inactive analogs desoctapeptide insulin, bPTH-(3-34), and oxidized hPTH-(1-34), or by calcitonin or IGF-II. The data suggest that insulin and PTH have a specific stimulatory effect on (Ca2+ + Mg2+)ATPase activity in canine kidney proximal tubular BLM. While the insulin action is independent of cAMP, a role of cAMP in the regulatory effect of PTH on this enzyme cannot be ruled out. The direct stimulatory effect of insulin and PTH on (Ca2+ + Mg2+)ATPase in canine kidney proximal tubular BLM suggests that these hormones mediate their cellular effects in part by changes in cellular calcium homeostasis.     

Ca(2+)-ATPase activity in streptozotocin-induced diabetic rat kidneys

Kidney Ca(2+)-ATPase activity was altered in streptozotocin (STZ)-induced diabetic rats. Male rats, 200-250 g, were rendered diabetic by injection of STZ 45 mg/kg body weight via the tail vein. Following injection, control rats and diabetic rats at 1, 4, 8 or 15 weeks were sacrificed. Kidney tissues were obtained for the isolation of Ca(2+)-ATPase. Ca(2+)-ATPase activity was determined spectrophotometrically. Total calcium was measured by atomic absorption spectrophotometry. Diabetic rats had significantly elevated blood glucose levels compared to controls. Blood glucose levels were 92.92 +/- 1.215 mg/dl (mean +/- S.E.M.) for the control group, and 362.50 +/- 9.613 mg/dl at one week and > 500 mg/dl at 4, 8 and 15 weeks of diabetes. Enzyme activities were significantly higher at 4, 8 and 15 weeks of diabetes than in the control group (p < 0.001). There was no significant increase at one week of diabetes. Ca(2+)-ATPase activity was 0.43 +/- 0.003 U/L, 0.517 +/- 0.058 U/L, 0.707 +/- 0.078 U/L, 0.730 +/- 0.006 U/L and 0.715 +/- 0.055 U/L respectively for controls and rats at 1, 4, 8 and 15 weeks of diabetes. Calcium levels in diabetic rat kidneys were also significantly higher than for controls. The increase in enzyme activity may have been caused by higher calcium levels in diabetic kidneys resulting from a compensatory response of the enzyme to high levels of the ion.     

Effects of caloric restriction and aging on erythrocyte membrane Ca(2+)-ATPase activity in specific pathogen-free Fischer 344 rats.

Dietary caloric restriction extends life span in the Fischer 344 rat. The interaction of aging and caloric restriction was examined at the level of the plasma membrane transport-associated enzymes, Ca(2+)-adenosine triphosphatase (ATPase) and Na,K-ATPase, in the Fischer rat. Animals were in four age groups, ranging from 6.1 to 25.0 months, and were specific pathogen-free (SPF, barrier-raised). Results from male and female animals raised on an ad libitum diet were compared with those from rats that received 60% of the age-specific caloric intake of their ad lib littermates. The responses of erythrocyte membrane Ca(2+)-ATPase activity in vitro to thyroid hormone (L-thyroxine [T4]; 3,5,3'-triiodothyronine [T3]) and to purified calmodulin, a Ca(2+)-binding protein activator of Ca(2+)-ATPase, were measured. Erythrocyte membrane Na,K-ATPase was also compared in the two diet groups, as was plasma glucose. Plasma membrane Ca(2+)-ATPase activity in the absence of added thyroid hormone and calmodulin was significantly reduced in calorically restricted rats (-39%, P less than .001), compared with ad lib-fed animals, and the response was similar in the four age groups aged 6.1, 12.7, 17.0, and 25.0 months. In contrast, pooled (all ages) Ca(2+)-ATPase response in vitro to T4 and to T3 in calorically restricted animals was enhanced compared with the ad lib group (+62% and +58%, P less than .001, respectively). Calmodulin responsiveness of the enzyme was increased by 45% (P less than .001) in calorie-deprived animals, similar to the change in T4 and T3 responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ca(2+)-Mg(2+)-ATPase activity and ionized calcium in Type 2 diabetic patients with neuropathy

Ca(2+)-Mg(2+)-ATPase is an important regulator of intracellular calcium concentration and therefore, of erythrocyte deformability. We have investigated the possible relationship between Ca(2+)-Mg(2+)-ATPase activity (ATPase) and ionized calcium (Ca(2+)), in diabetic patients with peripheral neuropathy. A total of 104 Type 2 diabetic patients (57 neuropathic and 47 non-neuropathic) and 25 non-diabetic subjects were studied. After an overnight fast, blood was taken for Ca(2+)-Mg(2+)-ATPase activity, Ca(2+), Mg(2+), PTH and HbA(1c). The neuropathy study group had significantly lower levels of ATPase, 6.6 (95% CI, 5.6-7.7) nmol/mg/min compared to controls 7. 1 (6.2-8.3) nmol/mg/min, P<0.001 and to diabetic patients without neuropathy 7.0 (6.0-8.1) nmol/mg/min, P<0.001. The study group had also lower levels of Ca(2+) (0.89+/-0.18 mmol/l vs. control 1.08+/-0. 24 mmol/l, P<0.01 and non-neuropathic 0.98+/-0.27 mmol/l, P<0.05) and Mg(2+) (0.73+/-0.13 mmol/l vs. control 0.81+/-0.14 mmol/l, P<0. 05), despite similar PTH levels. In diabetic subjects, no correlation was found between ATPase or Ca(2+) with glucose, HbA(1c), age or duration of diabetes. We conclude that in patients with diabetic neuropathy there are abnormalities of Ca(2+)-Mg(2+)-ATPase activity and Ca(2+). This provides further support for the role of microangiopathy in the pathogenesis of neuropathy.     

Increased susceptibility of the sickle cell membrane Ca2+ + Mg(2+)-ATPase to t-butylhydroperoxide: protective effects of ascorbate and desferal.

Normal and sickle cell erythrocyte membranes were examined for significant differences in their ATPase activities, thiobarbituric acid reactive products formed (measured relative to malondialdehyde), membrane protein polymerization, and number of protein-free sulfhydryl groups when treated with 0.5 mmol/L t-butylhydroperoxide (tBHP) for 30 minutes. Isolated sickle cell membranes treated with tBHP produced significantly greater inhibition in both their basal and calmodulin-stimulated Ca2+ + Mg(2+)-ATPase activities (75% inhibition in both cases) compared with that of control membranes. In addition, there was significantly more malondialdehyde formed from sickle cell membranes compared with control membranes. Oxidation caused greater protein polymerization in sickle cell membranes compared with normal membranes as demonstrated by the formation of high molecular weight polymers separated on sodium dodecyl sulfate polyacrylamide gels. The number of free sulfhydryl groups present in spectrin and actin decreased more in sickle cell membranes as measured by 3H-N-ethyl maleimide autoradiography and gel scanning. To prevent enzyme inhibition, erythrocyte membranes were treated with tBHP in the presence of 1 mmol/L ascorbate, a potential antioxidant, and 1 mmol/L desferal, an iron chelator. Both ascorbate and desferal added alone with tBHP were effective in preventing inhibition of the basal and calmodulin-stimulated Ca2+ + Mg(2+)-ATPase activities in normal membranes, but in sickle cell membranes only the addition of ascorbate and desferal together offered significant protection. The enhanced oxidation observed with sickle cell membranes can be mimicked in normal white membranes by adding hemoglobin, hemin, or ferrous chloride in the presence of tBHP. In contrast to hemoglobin, ferrous chloride has the ability to enhance membrane oxidation in the presence of ascorbate with or without tBHP. Furthermore, the addition of desferal to these membranes greatly decreased the iron-ascorbate-tBHP oxidation of erythrocyte membranes as determined by the sustained ATPase activities and the reduced formation of malondialdehyde. Maximal protection was provided by 1 mmol/L desferal in the presence of 1 mmol/L ascorbate, although some protection was observed even at 10 mumol/L, the lowest concentration tested. These results are discussed in light of the pro- and anti-oxidant effects of ascorbate in the absence and presence of iron and tBHP.     

Diminished expression of sarcoplasmic reticulum Ca(2+)-ATPase and ryanodine sensitive Ca(2+)Channel mRNA in streptozotocin-induced diabetic rat heart

The diabetic heart has an abnormal intracellular calcium ([Ca(2+)]i) metabolism. However, the responsible molecular mechanisms are unclear. The present study aimed to investigate mRNAs expressed in the proteins which regulate heart [Ca(2+)]i metabolism in streptozotocin (STZ)-induced diabetic rats. Expression of sarcoplasmic reticulum Ca(2+)-adenosine triphosphatase (SR Ca(2+)-ATPase) mRNA was significantly less in the heart 3 weeks after STZ injection than that in the age-matched controls. Together with the down-regulation of SR Ca(2+)-ATPase, expression of ryanodine sensitive Ca(2+)channel (RYR) mRNA was also decreased 12 weeks after STZ injection. Insulin supplementation fully restored the decreased mRNAs expression of SR Ca(2+)-ATPase and RYR. The diminished expression and restoration with insulin supplementation of SR Ca(2+)-ATPase was further confirmed at the protein level. In contrast, expression of mRNAs coding the L-type Ca(2+)channel, Na(+)-Ca(2+)exchanger, or phospholamban were not affected 3 or 12 weeks after STZ injection. These results can be taken to indicate that the down-regulation of SR Ca(2+)-ATPase and RYR mRNAs is a possible underlying cause of cardiac dysfunction in STZ-induced diabetic rats.     

(Ca2++Mg2+)-ATPase activity of sickle cell membranes: decreased activation by red blood cell cytoplasmic activator.

Human red blood cells (RBCs) contain a cytoplasmic protein that activates membrane-bound (Ca2+ + Mg2+)-ATPase and the transport of Ca2+. The (Ca2+ + Mg2+)-ATPase of sickle cells showed a less than normal response to this activator. This was true whether the activator was obtained from normal or sickle cells. Activator present in sickle cell hemolysates fully activated the (Ca2+ + Mg2+)-ATPase of normal RBC membranes. These results demonstrate that membranes of sickle cells are defective in their response to the activator. Neither the apparent affinity for calcium nor the apparent affinity for activator was different comparing the (Ca2+ + Mg2+)-ATPase of sickle and normal membranes. Young, mature, and irreversibly sickled cells were separated by density gradient centrifugation, and membranes were prepared from each of these cell populations. No significant differences in ATPase activities were found based on cell age (density). The (Ca2+ + Mg2+)-ATPase of all populations of sickle cells showed a decreased response to the activator. Thus, it appears unlikely that the decreased response of the (Ca2+ + Mg2+)-ATPase of sickle cells is due to membrane damage caused by repeated sickling during the life-span of the cell. Reduced activation of (Ca2+ + Mg2+)-ATPase by the cytoplasmic activator may account for calcium accumulation in sickle cells.     

Effects of an intracellular Ca(2+) chelator on insulin resistance and hypertension in high-fat-fed rats and spontaneously hypertensive rats

We explored the possibility that a sustained elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) may be a cellular abnormality common to both insulin resistance and hypertension. In high-fat diet (HFD) fed rats, the steady-state glucose infusion rate (GIR) during the euglycemic hyperinsulinemic clamp was reduced by 40% (P <.05) and mean arterial pressure (MAP) was elevated by 20 mm Hg (P <.01) in comparison to the normal chow-fed rats. Intravenous injection of 5,5'-dimethyl derivative of bis(o-aminophenoxy)ethane-N,N,N',N' tetraacetic acetoxymethyl ester (dimethyl-BAPTA/AM), an effective intracellular Ca(2+) chelator, 90 minutes before the clamp not only restored about 50% of the reduced GIR, but also normalized MAP in the HFD rats. The chelator injection also significantly increased GIR by 25% (P <.01) and reduced MAP about 30 mm Hg (P <.01) in the spontaneously hypertensive rats (SHR). In addition, we have recently shown in the HFD rats that an injection of dimethyl-BAPTA/AM normalizes elevated [Ca(2+)](i) in adipocytes. These results together demonstrate that lowering [Ca(2+)](i) simultaneously ameliorates both insulin resistance and hypertension and provide presumptive evidence that sustained high levels of [Ca(2+)](i) may play a common pathophysiologic role in these 2 diseases.     

Correlation between Ca(2+)-ATPase activity of rat islet cells and insulin secretion.

Using medium with a low ionic strength, a low concentration of Ca2+ and Mg2+ and devoid of K+, we have measured Ca(2+)-ATPase activity in the homogenates of rat islets preincubated for 3 min with several hormones in the presence of 3.3 mmol glucose/l. Insulin secretion was also measured in islets incubated for 5 min under identical experimental conditions. Islets preincubated with glucose (3.3 mmol/l) and glucagon (1.4 mumol/l) plus theophylline (10 mmol/l), ACTH (0.11 nmol/l), bovine GH (0.46 mumol/l), prolactin (0.2 mumol/l) or tri-iodothyronine (1.0 nmol/l) have significantly lower Ca(2+)-ATPase activity than those preincubated with only 3.3 mmol glucose/l. All these hormones increased the release of insulin significantly. Dexamethasone (0.1 mumol/l) and somatostatin (1.2 mumol/l) enhanced the Ca(2+)-ATPase activity while adrenaline (10 mumol/l) did not produce any significant effect on the activity of the enzyme. These hormones decreased the release of insulin significantly. These results demonstrated that islet Ca(2+)-ATPase activity was modulated by the hormones tested. Their inhibitory or enhancing effect seemed to be related to their effect on insulin secretion; i.e. those which stimulated the secretion of insulin inhibited the activity of the enzyme and vice versa. Hence, their effect on insulin secretion may be due, in part, to their effect on enzyme activity and consequently on the concentration of cytosolic Ca2+. These results reinforce the assumption that Ca(2+)-ATPase activity participates in the physiological regulation of insulin secretion, being one of the cellular targets for several agents which affect this process.     

高盐饮食对大鼠大脑皮质氧化应激及钠钙泵活性的影响

目的探讨长期高盐饮食对大鼠大脑皮质氧化应激和Na+-K+-ATPase、Ca2+-ATPase活性及其相关基因表达的影响。方法雄性Wistar大鼠随机分为正常盐对照组(NS组,n=13)、8%高盐组(HS组,n=24)和8%高盐+替米沙坦干预组(HS+Tel组,n=12),每2 w测量尾动脉压1次,喂养共24 w。比色法测定大鼠大脑皮质丙二醛(MDA)含量和超氧化物歧化酶(SOD)酶活性;用生化酶学法检测大脑皮质Na+-K+-ATPase、Ca2+-ATPase活性;通过实时荧光定量PCR法检测大脑皮质NAPDH、Na+-K+-ATPaseα1、细胞质膜钙泵(PMCA)1、钠钙交换蛋白(NCX)1和NADPH氧化酶亚单位P22phox mRNA表达。结果与NS组比较,HS组MDA含量增加、SOD活性减弱(P0.05),Na+-K+-ATPase、Ca2+-ATPase活性均降低(P0.05),NADPH氧化酶亚单位P22phox、Na+-K+-ATPaseα1、PMCA1 mRNA表达增加(P0.05),NCX1mRNA表达无明显变化;与HS组比较,HS+Tel组Na+-K+-ATPase、Ca2+-ATPase活性升高(P0.05),其他指标无明显改变。结论高盐饮食可引起大鼠大脑皮质氧化损伤及钠钙泵活性降低。     

Insulin antagonistic effects of insulin receptor antibodies on plasma membrane (Ca2+ + Mg2+) ATPase activity: a possible etiology of type B insulin resistance

The regulatory effect of insulin on plasma membrane (Ca2+ + Mg2+)ATPase activity in target tissues for insulin was proposed to be of importance in mediating the hormone's cellular action. Consequently, polyclonal insulin receptor antibodies from patients with type B insulin resistance (B7 and B10) were used as probes to further explore a possible role for this ATPase in insulin action. The antibodies B7 and B10 obtained during the active phase of the disease manifested insulinomimetic actions in rat renal cortical basolateral membranes by displacing [125I]insulin bound to the membranes and stimulating the tyrosine kinase activity of solubilized insulin receptors in a dose-dependent manner. In contrast, these antibodies had insulin antagonistic effects on the membrane (Ca2+ + Mg2+)ATPase activity. While insulin stimulated, both antibodies inhibited the ATPase basal activity in a dose-dependent manner. Furthermore, the stimulatory effect of insulin on the ATPase was completely abolished by the antibodies. Immunoglobulin fractions obtained from patient B10 in the clinically inactive phase of the disease and from pooled normal human sera did not affect basal or insulin-stimulated ATPase activity. The effects of insulin receptor antibodies on basal and insulin-stimulated (Ca2+ + Mg2+)ATPase activities were specific. The receptor antibody did not affect PTH-stimulated (Ca2+ + Mg2+) ATPase activity, nor did it affect other kidney basolateral membrane ATPase basal activities. The data reveal that insulin receptor antibodies have a direct regulatory effect on the plasma membrane (Ca2+ + Mg2+) ATPase. We suggest that the insulin antagonistic effects of the insulin receptor antibodies on the ATPase might explain in part the impaired insulin action in type B insulin resistance.     

Erythrocyte (Ca+2 + Mg+2)-ATPase activity: increased sensitivity to oxidative stress in glucose-6-phosphate dehydrogenase deficiency

The effect of the thiol-oxidizing agent diamide on erythrocyte (Ca+2 + Mg+2)-ATPase activity was measured in normal and glucose-6-phosphate-dehydrogenase-deficient (G6PD-) cells. Although the enzyme activity before the oxidative stress was similar in both groups, diamide induced a markedly greater inhibition in the enzyme activity in the G6PD- cells than in the normal controls. These data indicate dependence of erythrocyte (Ca+2 + Mg+2)-ATPase, in part, on the redox status of the cell. The increased vulnerability of (Ca+2 + Mg+2)-ATPase to oxidative stress in G6PD- may be of pathophysiological relevance to their premature destruction in oxidant-induced hemolysis.     

Crosslinking the active site of sarcoplasmic reticulum Ca(2+)-ATPase completely blocks Ca2+ release to the vesicle lumen.

Intramolecular crosslinking of the active site of the sarcoplasmic reticulum Ca(2+)-ATPase with glutaraldehyde results in substantial inhibition of ATPase activity and stabilization of the ADP-sensitive E1 approximately P(2Ca) intermediate (E, enzyme) with occluded Ca2+ [Ross, D. C., Davidson, G. A. & McIntosh, D. B. (1991) J. Biol. Chem. 266, 4613-4621]. We show here, using conditions of low passive vesicle permeability and absence of ADP, that Ca2+ "deoccludes" more rapidly than it leaks out of the vesicle lumen. Deocclusion is paralleled by dephosphorylation. Therefore, turnover of crosslinked E1 approximately P(Ca) (approximately 5 nmol/min per mg of protein at 25 degrees C) involves Ca2+ release to the vesicle exterior and concomitant phosphoenzyme hydrolysis. Ca2+ release to the lumen, the normal pathway, is apparently blocked completely. In the presence of ADP, Ca2+ is also released to the vesicle exterior, and this release is coupled to the synthesis of ATP. The results suggest that a tertiary structural change at the active site follows phosphorylation and is an absolute requirement for Ca2+ release from the native enzyme to the vesicle lumen.     

Improvement of insulin sensitivity by chelation of intracellular Ca(2+) in high-fat-fed rats

It has been postulated that sustained high levels of intracellular calcium concentration ([Ca(2+)](i)) in the insulin target cells may cause insulin resistance. We evaluated this hypothesis by examining the effect of an intracellular Ca(2+) chelator, 5,5'-dimethyl derivative of bis (o-aminophenoxy) ethane-N,N,N',N' tetraacetic acetoxymethyl ester (dimethyl-BAPTA/AM), on insulin resistance. Insulin resistance was induced in rats by feeding a high-fat diet for 3 to 4 weeks. The whole body insulin sensitivity was determined by the steady state glucose infusion rate (GIR) under euglycemic hyperinsulinemic (6 mU x kg(-1) x min(-1)) clamps. Compared with control rats, the high-fat diet (HFD) fed rats showed significantly lower GIR (12.2 +/- 0.7 v 20.2 +/- 0.9 mg x kg(-1) x min(-1); P <.01). In the HFD rats, an intravenous injection of dimethyl-BAPTA/AM (6 mg/kg) 90 minutes before the clamps significantly increased GIR to 16.3 +/- 0.9 mg x kg(-1) x min(-1) (P <.02), reversing insulin resistance by about 50%; but this intervention had no effect in the controls. This increase in GIR by dimethyl-BAPTA/AM was observed without an increase in femoral artery blood flow, indicating that the chelator increased GIR directly through improving cellular responsiveness to insulin. The stimulatory effect of insulin on 2-deoxy glucose (2-DG) uptake by the isolated epididymal adipocytes was reduced by 35% in the HFD rats compared with the control rats (P <.01). Pretreatment of the HFD rats with dimethyl-BAPTA/AM restored 2-DG uptake to the level in the control rats. The direct measurement of [Ca(2+)](i) using fura-2/AM in isolated adipocytes showed that basal [Ca(2+)](i) was significantly higher in the HFD rats than in the control rats (145 +/- 11 v 112 +/- 9 nmol/L; P <.05). An injection of dimethyl-BAPTA/AM in the HFD rats lowered [Ca(2+)](i) to 127 +/- 11 nmol/L, which did not differ from the level in the control rats (P >.2). The present study clearly demonstrates that an injection of intracellular Ca(2+) chelator in the HFD rats reverses insulin resistance, as well as normalizes elevated [Ca(2+)](i) in the insulin target cells. The results strongly support that sustained high levels of [Ca(2+)](i) in the insulin target cells may play an important role in insulin resistance, at least in the HFD rats.     

Alterations of Na+-K+-ATPase, Ca2+-ATPase, and Mg2+-ATPase activities in erythrocyte, muscle, and liver of traumatic and septic patients

Na+-K+-ATPase, Ca2+-ATPase and Mg2+-ATPase activities of erythrocyte membrane, microsomal fractions of rectus muscle, and liver were measured colorimetrically in the biopsy specimens of 14 control, 7 uncomplicated trauma (group 2), and 14 severe trauma or septic patients (groups 3-A and 3-B). In erythrocytes, these three ATPase activities in group 2 were not significantly changed but sepsis of both the acute (group 3-A) and ongoing type (group 3-B) decreased all of the ATPase activities. In muscle, there was a significant loss of three ATPase activities in the acute insult of severe trauma or sepsis (group 3-A), while Na+-K+-ATPase and Mg2+-ATPase activities were not significantly changed in ongoing, severe trauma (group 3-B). In the liver, a tendency for all three ATPase activities to decrease is noted in the severe traumatic group. However, a statistical difference between the control and severe traumatic group showed only for Na+-K+ ATPase and Mg2+-ATPase in group 3-A and Ca2+-ATPase in group 3-B. Correlation coefficients between erythrocyte, muscle, and liver for three ATPase activities are between 0.4 and 0.5. The mechanism which alters ATPase activity remains unknown in this study, but it may account for the variation in traumatic insult, in hemodynamic and hormone changes, and in tissue energy stores.     

Regulation of Ca2+-Mg2+-ATPase activity in hepatocyte plasma membranes by vasopressin and phenylephrine

A high affinity Ca2+-stimulated, Mg2+-dependent ATPase (Ca2+-Mg2+-ATPase) was identified in microsomes and plasma membrane vesicles isolated from rat hepatocytes. The distribution of this enzyme was similar to that of the plasma membrane marker enzymes alkaline phosphodiesterase and 5'-nucleotidase. The Ca2+-Mg2+-ATPase had an apparent half-saturation constant of approximately 75 nM for Ca2+. After incubation of rat hepatocytes with 25 nM vasopressin for 3 min, the activity of Ca2+-Mg2+-ATPase was decreased 15-30%. The effect of vasopressin on the activity of this enzyme was near maximal after incubating hepatocytes with vasopressin for only 15 sec. The concentration of vasopressin needed for half-maximal inhibition of this enzyme in hepatocytes was approximately 6 nM. Treatment of the hepatocytes with 10 microM phenylephrine caused about a 10% decrease in ATPase activity while 10 nM glucagon or 200 microU/ml insulin did not affect the enzyme. These findings suggest that inhibition of the Ca2+-Mg2+-ATPase activity may be part of the mechanism by which vasopressin and alpha-adrenergic agonists elevate cytosolic Ca2+ in hepatocytes.     

胰岛素治疗对2型糖尿病大鼠肝脂质含量及胰岛素抵抗的影响

目的探讨胰岛素治疗对2型糖尿病大鼠肝内脂质含量及胰岛素抵抗的影响。方法尾静脉注射小剂量链脲佐菌素(2 5 mg/kg) 高热量饮食建立2型糖尿病大鼠模型,根据口服葡萄糖耐量试验(OGTT) 和胰岛素分泌试验(IST)结果将其分为糖尿病非治疗(DC)组和糖尿病胰岛素治疗(DI)组,并设立正常对照(N C)组。胰岛素和等渗盐水干预4周后再行OGTT和IST,并检测各组大鼠的血脂、肝脂质及肝组织学改变。采用胰岛素敏感性指数(ISI)来评价胰岛素抵抗。结果D C组血脂、肝脂质含量明显高于NC 组(t值为2.59～1 5.77,P<0.05),而ISI则低于NC组(t=3.1 6,P<0.05),并且肝组织切片中出现明显的脂肪滴;与DC组相比,D I组血脂降低,而肝脂质显著增加(甘油三酯、胆固醇、游离脂肪酸分别增加55.70%,19.87%,22.20%),病理组织学检查显示脂肪滴增大融合,但是ISI变化不明显。结论2型糖尿病大鼠胰岛素治疗纠正血糖的同时增加了肝细胞内脂质的含量,但对胰岛素抵抗的影响不明显。     

Increase in Ca2+ (Mg2+)-ATPase activity induced by a molsidomine derivative (SIN-1 A) and nitroglycerin in microsomal fraction of guinea-pig thoracic aorta

The amount of phosphoric acid liberated from ATP by Ca2+ (Mg2+)-ATPase in microsomal fraction of guinea-pig thoracic aorta decreased with decreasing concentrations of calcium ions from 20.0 to 2.5 mM in the mixture of the enzyme and substrate. When CaCl2 (2.5 mM) and MgCl2 (5.0 mM) were present in the substrate, both nitroglycerin (0.1 to 1.0 mM) and SIN-1 A (a molsidomine derivative, 0.05 to 1.0 mM) increased the liberated phosphoric acid in a concentration-dependent manner. The contractile tension of smooth muscle prepared from guinea-pig thoracic aorta, which was previously increased by the pretreatment with prostaglandin F2 alpha (5.0 microM), was relaxed by both nitroglycerin and SIN-1 A (0.01 to 100 microM each) in a concentration-dependent manner. From the results, it is assumed that the stimulation of Ca2+ (Mg2+)-ATPase [Ca2+-pump ATPase] activity induced by nitroglycerin and SIN-1 A in the microsome of thoracic aorta takes part in the relaxation of contractile tension in the tissue.