Over three decades ago, Parker and Snow (Am J Physiol 223: 888-893, 1972) demonstrated that canine erythrocytes undergo an increase in cation permeability when incubated with extracellular ATP. In this study we examined the expression and function of the channel/pore-forming P2X(7) receptor on canine erythrocytes. P2X(7) receptors were detected on canine erythrocytes by immunocytochemistry and immunoblotting. Extracellular ATP induced (86)Rb(+) (K(+)) efflux from canine erythrocytes that was 20 times greater than that from human erythrocytes. The P2X(7) agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine 5'-trisphosphate (BzATP) was more potent than ATP, and both stimulated (86)Rb(+) efflux from erythrocytes in a dose-dependent fashion with EC(50) values of approximately 7 and approximately 309 microM, respectively. 2-Methylthioadenosine 5'-triphosphate and adenosine 5'-O-(3-thiotriphosphate) induced a smaller (86)Rb(+) efflux from erythrocytes, whereas ADP, AMP, UTP, or adenosine had no effect. ATP-induced (86)Rb(+) efflux from erythrocytes was inhibited by oxidized ATP, KN-62, and Brilliant blue G, known P2X(7) antagonists. ATP also induced uptake of choline(+) into canine erythrocytes that was 60 times greater than that into human erythrocytes. Overnight incubation of canine erythrocytes with ATP and BzATP induced phosphatidylserine exposure in >80% of cells and caused up to 20% hemolysis. In contrast, <30% of human erythrocytes showed phosphatidylserine exposure after overnight incubation with ATP and BzATP, and hemolysis was negligible. Flow cytometric measurements of ATP-induced ethidium(+) uptake showed that P2X(7) function was three times lower in canine monocytes than in human monocytes. These data show that the massive cation permeability increase induced by extracellular ATP in canine erythrocytes results from activation and opening of the P2X(7) receptor channel/pore.

We previously demonstrated that canine erythrocytes express the P2X 7 receptor, and that the function and expression of this receptor is greatly increased compared with human erythrocytes. Using 86 Rb + (K + ) and organic cation flux measurements, we further compared P2X 7 in erythrocytes and mononuclear leukocytes from these species. Concentration response curves of BzATP-and ATP-induced 86 Rb + efflux demonstrated that canine P2X 7 was less sensitive to inhibition by extracellular Na + ions compared to human P2X 7 . In contrast, canine and human P2X 7 showed a similar sensitivity to the P2X 7 antagonists KN-62 and Mg 2+ . KN-62 and Mg 2+ also inhibited ATPinduced choline + uptake into canine and human erythrocytes. BzATP and ATP but not ADP or NAD induced ethidium + uptake into canine monocytes, T-and B-cells. ATP-induced ethidium + uptake was twofold greater in canine T-cells compared to canine B-cells and monocytes. KN-62 inhibited the ATP-induced ethidium + uptake in each cell type. P2X 7 -mediated uptake of organic cations was 40-and fivefold greater in canine erythrocytes and lymphocytes (T-and B-cells), respectively, compared to equivalent human cell types. In contrast, P2X 7 function was threefold lower in canine monocytes compared to human monocytes.Thus, P2X 7 activation can induce the uptake of organic cations into canine erythrocytes and mononuclear leukocytes, but the relative levels of P2X 7 function differ to that of equivalent human cell types.

The saltwater crocodile is distributed throughout south-east Asia and Australia. In Australia, it is most abundant in the Northern Territory and Queensland, where it is sustainably farmed for its skins and meat. The aim of this study was to elucidate the relationships and genetic structure among saltwater crocodiles from the Northern Territory of Australia using mitochondrial control region sequences from 61 individuals, representing nine river basins and six of unknown origin, as well as published sequences from other regions. Eight mitochondrial control region haplotypes were identified among both published and novel sequences. Three of the haplotypes appear to be restricted to specimens from northern Australia, with a single haplotype being the most widely dispersed across all river basins. Although Analysis of Molecular Variance provides some support for differentiation among river basins, the frequency of shared haplotypes among these geographical units and median-joining network analysis do not support a clear genetic structure or phylogeographic pattern for saltwater crocodiles in the Northern Territory. The results of this study will assist in furthering our understanding of the genetic diversity of wild saltwater crocodile populations used for ranching in the Northern Territory, as well as providing a framework for assessing the origin of unknown specimens in the future.