Reduced Na+ + K+-ATPase activity in peripheral nerve of streptozotocin-diabetic rats: a role for protein kinase C?

Inhibition of aldose reductase attenuates endotoxin signals in human non-pigmented ciliary epithelial cells

Chronic inflammatory diseases such as autoimmune and bacterial infections are associated with an elevated risk of ocular inflammation. Ciliary epithelial cells that play an important role in maintaining aqueous humor dynamics and homeostasis of anterior segment of eye are continuously exposed to inflammatory markers during infections and injury. Lipopolysacchharide (LPS), a Gram-negative bacterial endotoxin, dysregulates aqueous humor (AqH) homeostasis by inducing inflammatory changes. We have investigated how inhibition of a polyol pathway enzyme, aldose reductase (AR), alters LPS-induced inflammatory changes in human non-pigmented ciliary epithelial cells (hNPECs). The stimulation of hNPECs with LPS (1 microg/ml) caused increased secretion of inflammatory markers such as PGE(2) and NO in the culture medium as well as increased expression of COX-2 and iNOS proteins in cell extracts. LPS also increased phosphorylation of MAPKs (ERK1/2) and SAPK/JNK and activation of redox-sensitive transcription factors NF-kappaB and AP-1 in hNPECs and inhibition of AR by zopolrestat and sorbinil ameliorated these changes. Further, LPS-induced decrease in the expression of Na/K-ATPase in hNPECs was restored by AR inhibitors. Similar results were observed in ciliary bodies of LPS-injected rats. Taken together, our results suggest that AR plays an important role in the LPS-induced inflammatory changes in hNPECs and that inhibition of AR could be a novel therapeutic approach for ocular inflammation.

Na(+)-K(+)-ATPase gene expression in the avian eggshell gland: distinct regulation in different cell types

The avian eggshell gland (ESG) is a tissue specialized in transporting the Ca(2+) required for eggshell formation and represents a unique biological system in which the calcification process takes place in a circadian fashion. With the use of RNA fingerprinting, a set of genes differentially induced at the time of calcification was detected, one of which was identified as the alpha(1)-subunit of Na(+)-K(+)-ATPase. The gene was expressed in a circadian manner in both cell types populating the ESG, but in different temporal patterns, suggesting distinct mechanisms of regulation. Ca(2+) flux and mechanical strain were found to regulate gene expression in the inner glandular epithelium and the pseudostratified epithelium facing the lumen, respectively. Mechanical strain also affected gene expression in cell layers facing the lumen in other parts of the oviduct. Only the alpha(1)-isoform, not the alpha(2)- or alpha(3)-isoform, of Na(+)-K(+)-ATPase was expressed in the ESG. In summary, we demonstrate that the alpha(1)-subunit Na(+)-K(+)-ATPase gene is expressed in different epithelial cell types in the ESG and is regulated by various mechanisms, which may reflect the disparity in the physiological roles of the cells in the process of eggshell formation.

The effects of dietary treatment with essential fatty acids on sciatic nerve conduction and activity of the Na+/K+ pump in streptozotocin-diabetic rats

1. This study examined the effects of dietary essential fatty acid supplementation (5% (w/w) evening primrose oil) upon sciatic motor nerve conduction velocity and 86Rb+ pumping in sciatic nerve endoneurial preparations in rats with 4 to 5 weeks of streptozotocin-induced diabetes. 2. Control diabetic rats (dietary supplementation with 5% (w/w) hydrogenated coconut oil) exhibited a reduction in motor nerve conduction velocity (16%; P less than 0.05) compared to similarly-fed non-diabetic controls, but there was no significant alteration in ouabain-sensitive 86Rb+ pumping, a parameter reflecting activity of the Na+/K+ pump. 3. Treatment of diabetic rats with evening primrose oil prevented completely the development of the motor nerve conduction velocity deficit without affecting the severity of diabetes. Evening primrose oil treatment did not significantly affect motor nerve conduction velocity of non-diabetic animals. 4. Evening primrose oil treatment caused a significant reduction in activity of the Na+/K+ pump in sciatic nerves of diabetic animals (45%; P less than 0.05). 5. These results suggest that the acute conduction velocity defect arising in streptozotocin-diabetic rats, and the actions of evening primrose oil upon this, are independent of any effect on activity of the Na+/K+ pump. Other putative mechanisms are discussed.

Diacylglycerol accumulation and microvascular abnormalities induced by elevated glucose levels

The present experiments were undertaken to examine the hypothesis that glucose-induced increased de novo synthesis of 1,2-diacyl-sn-glycerol (which has been observed in a number of different tissues, including retinal capillary endothelial cells exposed to elevated glucose levels in vitro) and associated activation of protein kinase C may play a role in mediating glucose-induced vascular functional changes. We report here that twice daily instillation of 30 mM glucose over 10 d in a rat skin chamber granulation tissue model induces approximately a 2.7-fold increase in diacylglycerol (DAG) levels (versus tissues exposed to 5 mM glucose) in association with marked increases in vascular clearance of albumin and blood flow. The glucose-induced increase in DAG levels as well as the vascular functional changes are prevented by addition of 3 mM pyruvate. Pharmacological activation of protein kinase C with the phorbol ester TPA in the presence of 5 mM glucose increases microvascular albumin clearance and blood flow, and similar effects are observed with 1-monoolein (MOG), a pharmacological inhibitor of the catabolism of endogenous DAG. A pharmacological inhibitor of protein kinase C (staurosporine) greatly attenuates the rise in microvascular albumin clearance (but not the rise in blood flow) induced by glucose or by MOG. These findings are compatible with the hypothesis that elevated concentrations of glucose increase tissue DAG content via de novo synthesis, resulting in protein kinase C activation, and that these biochemical events are among the factors that generate the increased microvascular albumin clearance.