In Vivo Measurement of Na+ and K+ ions Using ion-Selective Electrodes

摘要

Measurement of circulating levels of the electrolytes Na+ and K+ is integral tophysiological studies of hyperthermia, dehydration, and nutrition. Current methods require removal of blood samples for later analysis. In small animals such as rats the volume removed can alter experimental results. In this study, cannulae were surgically implanted in a jugular vein and carotid artery of rats. Using ion selective electrodes and a flow-through sampling chamber of our own design, in vivo measurements of circulating Na+ and K+ concentrations were made by connecting the arterial cannula to the inflow port and the jugular cannula to the outflow port of the sampling chamber. The sampling chamber, electrode apparatus and the cannulae require only 0.8 ml of extracorporeal blood. Although measurement of K+ concentration was abandoned because of continuous electrode drift, measurements of Na+ concentrations accurately reflected expected values following dilution of in vitro blood samples with solutions of known electrolyte concentrations and expected changes in vivo following administration of hypertonic solutions to the animals. Use of this apparatus should allow continuous measurement of Na+ concentration with minimal loss of blood volume in future studies.