Glass electrode measurement of ion transfers during rewarming of the single rat tail artery

Abstract

Capillary glass electrodes were used in two separate procedures to examine the kinetics of exchange of Na⁺ for K⁺ during rewarming of the precooled rat tail artery. In the first system, the intravascular medium remains stationary in the artery for intervals of 3, 6, or 9 min, and the change in ion concentrations in this small volume (approximately 25 × 10⁻³ ml) is then measured by difference against a parallel "dummy" system. In the second procedure, the intravascular medium moves continuously at 0.01 ml/min and is collected in fine bore polyethylene tubing for later passage through the electrodes at 0.15 ml/min. Both systems yielded similar quantitative data but the first system was less precise and it is possible that the artery was less well maintained. The second system clearly revealed an extra complement of Na⁺ liberated from the tissue well in advance of an observable, metabolically driven uptake of K⁺ and provided a detailed substantiation of previously reported deductions of this fact. The final equilibrium transcellular Na⁺ and K⁺ gradients attained after rewarming were lower in stretched than in unstretched arteries.