Renal ouabain inhibitable Na-K ATPase activity and myoinositol supplementation in experimental diabetes mellitus

Animal and human tissue Na,K-ATPase in normal and insulin-resistant states: regulation, behaviour and interpretative hypothesis on NEFA effects

The sodium(Na)- and potassium(K)-activated adenosine-triphosphatase (Na,K-ATPase) is a membrane enzyme that energizes the Na-pump by hydrolysing adenosine triphosphate and wasting energy as heat, so playing a role in thermogenesis and energy balance. Na,K-ATPase regulation by insulin is controversial; in tissue of hyperglycemic-hyperinsulinemic ob/ob mice, we reported a reduction, whereas in streptozotocin-treated hypoinsulinemic-diabetic Swiss and ob/ob mice we found an increased activity, which is against a genetic defect and suggests a regulation by hyperinsulinemia. In human adipose tissue from obese patients, Na,K-ATPase activity was reduced and negatively correlated with body mass index, oral glucose tolerance test-insulinemic area and blood pressure. We hypothesized that obesity is associated with tissue Na,K-ATPase reduction, apparently linked to hyperinsulinemia, which may repress or inactivate the enzyme, thus opposing thyroid hormones and influencing thermogenesis and obesity development. Insulin action on Na,K-ATPase, in vivo, might be mediated by the high level of non-esterified fatty acids, which are circulating enzyme inhibitors and increase in obesity, diabetes and hypertension. In this paper, we analyse animal and human tissue Na,K-ATPase, its level, and its regulation and behaviour in some hyperinsulinemic and insulin-resistant states; moreover, we discuss the link of the enzyme with non-esterified fatty acids and attempt to interpret and organize in a coherent view the whole body of the exhaustive literature on this complicated topic.

Suppression of sodium-dependent glucose uptake by captopril improves high-glucose-induced morphological and functional changes of cultured bovine retinal pericytes

The effects of captopril on glucose uptake, as well as morphological and functional changes of retinal pericytes, in a high-glucose medium were examined. Retinal pericytes were incubated in medium with 5 and 30 mM glucose and 30 mM glucose with 10(-6) to 10(-3) M captopril. Captopril decreased the cellular uptakes of d-glucose and alpha-methyl glucoside in the presence, but not in the absence, of sodium. The cellular size and contents of glucose, sorbitol, and fructose were increased in 30 mM glucose concomitant with the decreased thymidine, cellular DNA content, and ratios in glucose to sorbitol and to fructose, compared with those in 5 mM glucose. These changes observed in 30 mM glucose were reversed by 10(-4) M captopril. These data suggest that the suppression of d-glucose uptake through a sodium-coupled glucose transporter by captopril may attenuate the swelling and loss of pericytes observed in the early stage of diabetic retinopathy.

Normalization of glucose entry under the high glucose condition by phlorizin attenuates the high glucose-induced morphological and functional changes of cultured bovine retinal pericytes

We previously reported that sodium-dependent glucose uptake is present in bovine retinal pericytes and that phlorizin normalizes its glucose consumption under high glucose conditions. To clarify the effect of phlorizin on morphological and functional change of retinal pericytes under high glucose conditions, retinal pericytes were incubated in media with 5 mM glucose, 30 mM glucose, and 30 mM glucose plus 0.2 mM phlorizin for 7 days. The diameter of cells in the concentrations of glucose more than 10 mM were significantly larger than those in 5 mM glucose and 30 mM glucose plus phlorizin. Glucose, sorbitol and fructose contents of the cells in 30 mM glucose were significantly increased compared with those in 5 mM glucose, and were normalized by phlorizin. Thymidine uptake in the concentrations of glucose more than 20 mM was significantly decreased compared with that in 5 mM glucose. Myoinositol uptake, and DNA in 30 mM glucose were significantly reduced, and were normalized with phlorizin. Myoinositol content in 30 mM glucose was the same as that in 5 mM glucose, but was significantly decreased by phlorizin. The ratios of glucose to sorbitol or fructose in 30 mM glucose were significantly decreased, compared with those in 5 mM glucose and 30 mM glucose plus phlorizin. Therefore, the cellular enlargement and decreased DNA synthesis in cultured bovine retinal pericytes with abnormal glucose metabolism under high glucose conditions are attenuated by phlorizin, independent of the cellular myoinositol content.