This study was conducted to evaluate the influence of proinsulin C-peptide on erythrocyte Na + ,K + -ATPase and endothelial nitric oxide synthase activities in patients with type I diabetes. In a randomized double-blind study design, ten patients with type I diabetes received intravenous infusions of either human C-peptide or physiological saline on two different occasions. C-peptide was infused at a rate of 3 pmol·min -1 ·kg -1 for 60 min, and thereafter at 10 pmol·min -1 ·kg -1 for 60 min. At baseline and after 60 and 120 min, laser Doppler flow (LDF) was measured following acetylcholine iontophoresis or mild thermal stimulation (44 °C), and venous blood samples were collected to determine plasma cGMP levels and erythrocyte membrane Na + ,K + -ATPase activity. The LDF response to acetylcholine increased during C-peptide infusion and decreased during saline infusion [18.6±19.2 and -13.2±9.4 arbitrary units respectively; mean±S.E.M.; P < 0.05). No significant change in LDF was observed after thermal stimulation. The baseline plasma concentration of cGMP was 5.5±0.6 nmol·l -1 ; this rose to 6.8±0.9 nmol·l -1 during C-peptide infusion ( P < 0.05). Erythrocyte Na + ,K + -ATPase activity increased from 140±29 nmol of P i ·h -1 ·mg -1 in the basal state to 287±5 nmol of P i ·h -1 ·mg -1 during C-peptide infusion ( P < 0.01). There was a significant linear relationship between plasma C-peptide levels and erythrocyte Na + ,K + -ATPase activity during the C-peptide infusion ( r = 0.46, P < 0.01). No significant changes in plasma cGMP levels or Na + ,K + -ATPase activity were observed during saline infusion. This study demonstrates an effect of human proinsulin C-peptide on microvascular function, which might be mediated by an increase in NO production and an activation of the erythrocyte Na + ,K + -ATPase. These mechanisms are compatible with the previous observed microvascular effects of C-peptide in patients with type I diabetes.

1. Na+,K+-ATPase activity and its α 1 subunit protein and mRNA in kidney cortex were monitored in rats developing Fanconi syndrome after the administration of maleate. Na+,K+-ATPase activity was significantly lower than in saline-injected controls, although this was partially mediated by a general, non-specific decrease in the cortex protein content. 2. The low activity of the sodium pump correlated with low abundance of α 1 subunit mRNA and protein levels. Hsp60 protein levels were also decreased in kidney cortex from maleate-treated rats. 3. Kidney cortex brush-border membrane vesicles from maleate-treated rats showed a marked decrease in Na+-dependent alanine and glucose transport, which was not dependent on the Na + -transmembrane gradient itself, a finding which is consistent with a more stable effect at the plasma membrane level. 4. The effect of maleate may be partially nonspecific and involve a great variety of proteins, but seems to be restricted to selected tissues because α 1 subunit Na+,K+-ATPase and hsp60 protein amounts were not significantly modified in livers from rats developing Fanconi syndrome. 5. These results show that maleate administration induces a low activity of selected concentrative transport systems and a decrease in Na+,K+-ATPase activity and expression. The combination of both effects may explain the increased excretion of most organic solutes present in rats developing Fanconi syndrome.

1. Na + ,K + -ATPase is the membrane enzyme catalysing the active transport of Na + and K + across the plasma membrane of animal cells. A reduced activity of Na + ,K + -ATPase has been described in gestational hypertension in a variety of cell types, in agreement with the hypothesis that gestational hypertension can induce membrane transport modifications similar to those reported for essential hypertension. The causes of the reduced Na + ,K + -ATPase activity are still debated. 2. The aim of the present work was to investigate the molecular mechanism of the reduced enzymic activity in gestational hypertension using as a model Na + ,K + -ATPase purified from human placenta. Na + ,K + -ATPase obtained from term placentas of eight healthy pregnant women and eight age-matched women with gestational hypertension was purified as previously described. 3. We observed in gestational hypertension: (i) a significant increase in the activation energies above transition temperature; (ii) a significant decrease in the fluorescence polarization of 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (i.e. increased fluidity) and an increase in the mean lifetime (modified hydrophobicity); (iii) a lower K q , suggesting an enzymic structural modification; and (iv) an increased mean lifetime and rotational relaxation time of pyrene isothiocyanate, indicating a modified ATP binding site.

1. Previously we have shown that sera from patients with fulminant hepatic failure (FHF) will inhibit partially purified rat brain Na + ,K + -ATPase and sodium efflux from human leucocytes in vitro . Similar inhibition may be involved in the pathogenesis of encephalopathy and cerebral oedema in these patients. 2. In the present study we have attempted to establish whether the activity of brain Na + ,K + -ATPase is decreased in vivo in rats with d -galactosamine induced hepatic failure using homogenates of snap-frozen brains. 3. Na + ,K + -ATPase activity was significantly reduced in the forebrain region at the stage of mild encephalopathy (43 h after injection), while at the deeper stage of coma (43–53 h after injection) enzyme activity was further reduced in the forebrain region and was also significantly reduced in the hindbrain region. Ouabain insensitive ATPase activity was not significantly altered at any time. 4. While a significant increase in the water content (0.5%) of the hindbrain region was found 43 h after galactosamine, there was no clear correlation between the development of cerebral oedema and the reduction of Na + ,K + -ATPase activity. 5. The activity of partially purified normal rat brain Na + ,K + -ATPase was 15% lower when incubated with sera from rats in the deep stage of coma compared with control sera. 6. These data support other evidence that the reduction in brain Na + ,K + -ATPase is likely to be due to toxic substance circulating in serum which have been shown to inhibit this enzyme in vitro and to cause coma when administered to normal animals.

1. Total and Na + ,K + -ATPase activities have been measured in sections (10 μm thick) from blocks of rat kidney cultured for 5 h at 37°C, pH 7.5, in Glasgow Eagle's Minimum Essential Medium. 2. Synthetic [arginine]vasopressin ([Arg]VP) stimulated ATPase activity in the thick tubular cells of the renal outer medulla over the concentration range 0.01-10 fmol/l, but failed to affect ATPase activity in the proximal and distal convoluted tubules of the cortex. 3. The increase in medullary total ATPase activity induced by [Arg]VP and its analogues was wholly due to stimulation of Na + ,K + -ATPase activity. 4. Stimulation of medullary ATPase activity was blocked by [Arg]VP antiserum. 5. The [Arg]VP analogues desmopressin, [lysine]vasopressin, [arginine]vasotocin and oxytocin stimulated medullary Na + ,K + -ATPase activity, the three last-named analogues being considerably less potent than [Arg]VP.

1. In order to study cation transport in vivo we have measured the changes in plasma and intra-erythrocytic rubidium concentrations following an oral load of rubidium chloride. The changes in plasma rubidium concentration are related to the distribution of rubidium to all the body tissues and the changes in intra-erythrocytic rubidium concentrations provide an example of rubidium uptake by one particular tissue. 2. In eight healthy volunteers pretreatment with a loading dose of digoxin (20 μg/kg) enhanced the rise in plasma rubidium concentrations and attenuated the rise in intra-erythrocytic rubidium concentrations after the oral load of rubidium chloride. 3. Ten patients with chronic renal failure, compared with a well-matched control group, were found to have changes similar to, but more marked than, those caused by digoxin, i.e. a much greater rise in plasma rubidium concentrations and a much smaller rise in intra-erythrocytic rubidium concentrations, after the oral load of rubidium chloride. 4. These findings are consistent with widespread reduction in Na + ,K + -ATPase activity in subjects who have taken a loading dose of digoxin and patients with chronic renal failure. They are, therefore, consistent with the findings of previous studies in vitro and show that it is possible to demonstrate changes in cation transport in vivo .