A novel microflow technique is used to demonstrate that a weakened oxidant defense system found in diabetic erythrocytes leads to decreased levels of deformation-induced release of adenosine triphosphate (ATP) from erythrocytes. Addition of an oxidant to rabbit erythrocytes resulted in a 63% decrease in deformation-induced ATP release before eventually recovering to a value that was statistically equivalent to the initial value. Inhibition of glucose-6-phosphate dehydrogenase prevents recovery from the oxidant attack. Finally, results indicated that the ATP release from the erythrocytes of type II diabetics (91 nM +/- 10 nM) was less than half of that measured from the erythrocytes of healthy controls (190 +/- 10 nM). These data suggest that the antioxidant status of erythrocytes is a critical determinant in the ability of these cells to release ATP, a known nitric oxide stimulus.

ATP is a recognized stimulus of nitric oxide synthase and is released from red blood cells (RBCs) upon deformation. The objective of this work is to demonstrate that RBCs stimulate nitric oxide production in platelets by employing a continuous flow analysis system in which the stream contains both RBCs and platelets. Here, two drugs known to improve blood flow in vivo (pentoxyfilline and iloprost) are shown to increase both the release of RBC-derived ATP and the production of platelet-derived NO. A flowbased chemiluminescence assay (in vitro) was employed to quantitatively determine the amount of ATP released from erythrocytes subjected to flow-induced deformation. Prior to being subjected to flow, erythrocytes were incubated in the absence or presence of 4.8 µM pentoxyfilline or 80 nM iloprost. Erythrocytes obtained from rabbits (n ) 22) that were subjected to flow released 239 ( 29 nM ATP. When treated with pentoxyfilline, the ATP released from the flowing RBCs increased to 450 ( 94 nM ATP. An increase in RBC-derived ATP was also measured for iloprost-incubated RBCs in flow (362 ( 45 nM ATP). Importantly, platelets that were loaded with diaminofluorofluorescein diacetate, an intracellular fluorescence probe for NO, exhibited increases in fluorescence intensity by 16% in the presence of RBCs treated with pentoxyfilline and a 10% increase when treated with iloprost. When the ATP release from the RBCs was inhibited with glybenclamide, the platelet fluorescence intensity decreased by 25 and 51% for RBCs incubated with pentoxyfilline and iloprost, respectively. In an experiment not involving the RBC, inhibition of the P2x receptor on the platelets (an ATP receptor) resulted in no increase in platelet NO production, suggesting that the NO production in the activated platelet is due to ATP.In addition to its well-known ability as a vasodilator, NO is also able to inhibit platelet activation and aggregation. Platelets have also been shown to produce NO upon activation. 1 Freedman et al. simultaneously measured NO production and aggregation of platelets upon activation with ATP. 2 These authors placed an electrode for NO into the cell of an aggregometer in order to simultaneously monitor the NO release from platelets and the aggregation of the platelets, thus demonstrating that NO was produced and released by these cells upon activation. From these studies, the authors concluded that NO released by the platelets was key to preventing further platelet recruitment to the activated platelets, but only mildly prevented their adhesion to an endothelium.In question concerning the production and release of plateletderived NO is the mechanism by which the NO production is stimulated. For example, ATP is a recognized stimulus of nitric oxide synthase (NOS) and subsequent production of platelet NO; moreover, it is also known that ATP is released from platelets upon activation. 3 However, it has not been established if ATP released from activated platelets has the ability to stimulate the production of NO in platelets. Here, res...

Microdialysis is one of the most popular techniques for sampling biological molecules from living tissue. Dialysis is the process of sampling fluid in the in vivo environment, which uses a semi‐permeable membrane that allows endogenous biological molecules to diffuse into a sample via a concentrated gradient. This article focuses on microdialysis of the brain.