Lithium Substitution Analysis of Na and K Phases in a Small Artery

Abstract

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.

The effects of external sodium substitution on cell sodium and potassium in vascular smooth muscle

“…The measurement of cell Li In previous studies we have shown that the movement of Li or of Na across the vascular smooth muscle cell membrane is sufficiently slowed by low temperature to permit simple differentiation of cellular from extracellular locations of these ions (Friedman, 1974(Friedman, , 1975Friedman et al 1974 in this Li-enriching medium at 370 C for a further 1 hr. The samples were then rapidly placed in cold (30 C) PSS for intervals from 30 to 90 min to replace extracellular Li with Na before routine tissue processing.…”

“…All media were maintained at pH 7-4 with continuous aeration with 95 % 02, 5 % C02. The detailed composition and method of preparation of these solutions have been presented elsewhere (Friedman, Mar & Nakashima, 1974).…”

Sodium pump activity in arteries of Dahl salt-sensitive rats.

“…11 We tested this hypothesis in Dahl salt-sensitive (S) and salt-resistant (R) rats. 18 Because the pressure-natriuresis curve of kidneys of S rats is shifted toward the pressure axis, 14 one would expect that salt-feeding would result in salt and water retention sufficient to elevate arterial pressure. The results of the present study offer evidence that such volume-expansion does, in fact, occur.…”

“…18 In some rats from each group (R L = 6; R H = 5; S L = 7; S H = 6), blood urea nitrogen (autoanalyzer), serum creatinine (autoanalyzer), and sodium and potassium (flame photometer) concentrations were measured.…”

“…In the remaining nine rats, we used lithiumsubstitution procedures similar to those developed by Friedman et al 18 to estimate intracellular concentrations of Na + and K+ in freshly dissected (by D.D.K.) tail artery and thoracic aorta, sodium-loaded for 5 or 60 minutes as described above.…”