Compartments of sodium in a small artery

Abstract

Viable tail artery samples, in a modified Krebs medium, gain Na in exchange for K during cooling and reverse the process during rewarming. The process, within the margin of experimental error, is usually in a 1:1 ratio and has a long time constant, about 8 to 9 meq/100 g dry weight being exchanged within 3 h of cooling, and up to 15 meq/100 g within 24 h. Three hours of rewarming of tissues prepared by overnight (18 h) cooling is sufficient for an exchange of at least 10 meq/100 g. A second component of Na, equal to approximately 10 meq/100 g in tissue incubated in a Tris-buffered medium [Formula: see text], is apparently paracellular, for it is fully mobilized within 30 min of exposure to a sodium-free environment, even at 2°. Since even 3 h of exposure to such a medium at 2° fails to mobilize metabolism-dependent cellular Na it is possible to differentiate these two components. Evidence is also presented to show that Na transport, ordinarily associated with K accumulation, can occur without it.