Determination of ATP release from erythrocytes using microbore tubing as a model of resistance vessels in vivo

A biomimetic model is described for the detection of adenosine triphosphate (ATP) release from red blood cells (RBCs) as they traverse fused-silica tubing ranging in i.d. from 25 to 75,mum. A continuous flow system is employed to create stress on the RBCs once they have entered the microbore tubing. This stress induces release of RBC-derived ATP, which is known to stimulate nitric oxide production in endothelial cells, resulting in eventual dilation of arterial smooth muscle. In this study, the RBCs were subjected to variations in tubing length and inside diameter. In a 25-mum-i.d. tube, the amount of ATP released from the RBCs increased from 3.74 +/- 0.56 to 9.55 +/- 0.73 muM as the tubing length was increased from 35 to 100 cm. In addition, for a 100-cm-length tube, the amount of ATP released from the RBCs increased from 3.03 +/- 0.49 to 9.55 +/- 0.73 muM as the inside diameter of the tubing decreased from 75 to 25 mum. To demonstrate that the erythrocytes were not being lysed inside the fused-silica tubing, dog RBCs, which are known to contain amounts of ATP similar to those of rabbit but do not release that ATP under physiological conditions, were investigated. It was determined that the dog RBCs released <1 muM of ATP when passed through tubing with a 25-mum i.d. and a length of 100 cm.