Cell Na in the rat tail artery was measured by replacing all extracellular Na with Li at 2°C. Water was partitioned with 14C-sorbitol as the marker. The binding capacity of the cytoplasm was estimated by ion-exchange after the destruction of cell membranes by alternate freezing and thawing. Cell Na is of the order of 20–25 mEq/kg dry weight and about 2/3 of this may be in free solution with [Na]i in the range of 15 mEq/liter. Cell K is about 220 mEq/kg dry weight and, of this, 30 mEq or more is bound so that [K]i is not greater than 190 mEq/liter. These estimates allow only for the low figure of 30 mEq as the sum of site-bound cell monovalent cations. It is shown, however, that as much as 50-60 mEq may be site-bound or otherwise restricted within the cell. A similar amount, mostly Na+, is site-bound within the paracellular matrix.
Uninephrectomized rats were treated with DOCA-saline for 3 weeks. Active Na transport activity was assessed in the rat tail artery in three separate ways. In the first method, Na-K exchange was expressed in terms of steady-state values in normal and ouabain-blocked arteries. In the second method, the relation of free cell Na to [Na]0 was measured after equilibration in media in which [Na]0 varied from about 25 to 140 mM. In the third method, the relation of cell K to [k]0 was measured with glass electrodes during the reestablishment of normality following prolonged K depletion. All methods yielded evidence of enhanced net active transport activity in the incubated artery (zero intraluminal pressure) in steady state.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.