Identification of different sodium compartments from smooth muscle cells, fibroblasts and endothelial cells, in arteries and tissue culture

Abstract

SUMMARY1. The 22Na efflux curve from the rat tail artery, at 35 0C, can be analysed as the sum of three distinct components, from 0 to 90 min of washout. After an initial diffusional component the two late exponential components Be-kBt and Ce-ket have the following values: B = 3-03 + 0-15 m-mole/kg wet wt. and C = 0-56 + 0-04; kB = 0-145 + 0-005 min-and kc = 0-015 + 0-007.2. In order to identify the cellular origin of the different compartments we compared the 22Na efflux curve from the rat tail artery with the curves obtained from whole rabbit aortal strips, rabbit aortal medial or adventitial strips; and primary cultures from rabbit aorta medial smooth muscle cells, cultures of a non-fusing muscle cell line (BC3H1), libroblasts and endothelial cells. 4. The efflux from compartment B of smooth muscle cells is inhibited by ouabain and in the absence of extracellular K+. The efflux from compartment C is inhibited only by ouabain but not by the suppression of extracellular K+.5. We propose a distribution of Na+ in smooth muscle cells in two intracellular compartments: (1) Na+ freely dissolved in the sarcoplasm, exchanging with the kinetics of compartment B and (2) a second cellular compartment which could be contained in the sarcoplasmic reticulum exchanging with the kinetics of compartment C.* To whom correspondence and reprint requests should be sent. R. P. GARA Y AND OTHERS 6. On the basis of the previous model of Na+ distribution, considering our values, and without any correction, the estimated sarcoplasmic concentration of Na+ is 9-6 mm, compatible with the direct measurements obtained in skeletal and heart muscle. The Na+ concentration in the sarcoplasmic reticulum would be 4-10 times higher than in the cytoplasm. In order to increase the accuracy of our calculations it would be necessary to account for the interdiffusion and back diffusion of Na+ between compartments. It is not possible to attain this goal at the present time.

Sodium metabolism in rat resistance vessels.

“…The dry weight/smooth muscle cell volume ratio was 0-66 indicating that [Na]i was about 20 mmol kg-' dry weight. These values are of the same order as those found in rat aorta (12 mmol kg-' cellular water, Jones, 1974) and tail artery (25 mmol kg-' dry weight, Friedman, Mar & Nakashima, 1974; about 11 mmol kg-' cellular water, Garay, Moura, Osborne-Pellegrin, Papadimitriou & Worcel, 1979). They are, however, substantially smaller than those obtained from rabbit portal vein using electron-probe analysis (47 mmol kg-' cellular water, Somlyo, Somlyo & Shuman, 1979).…”

“…First, back-extrapolation of this phase gave a value for the zero time intercept of 13-5 mmol 1-1 cells, which is not different from that found for [Na]i using the cold Li method. Secondly, about 50 % of the phase is ouabain dependent, which is not different from that expected for the intracellular phase (Garay et al 1979). The main part of the ouabain-resistant efflux is probably a temperature-sensitive efflux, since the efflux in cold Li saline (see Methods) was only about 4 % of the total efflux.…”

“…The washout of Na into physiological saline at 37 0C can in larger arteries be split up into three phases (Garrahan, Villamil & Zadunaisky, 1965;Garay et al 1979), where phase 3 represents efflux from a very small compartment. We found, however, only two phases, probably because the method we have used is not sensitive enough to detect the third phase in the small vessels.…”

Mechanism of Action of Angiotensin Ii on Excitation‐contraction Coupling in the Rat Portal Vein

“…We decided to determine whether the increase in spontaneous activity induced by At II persisted in the presence of ouabain at concentrations which blocked the Na pump (Garay, Moura, Osborne-Pellegrin, Papadimitriou & Worcel, 1979). The addition of ouabain (103 M) to the normal perfusing medium containing 10 mM TEA produced a depolarization of 5 to 10 mV accompanied by an AP acceleration.…”

Direct action of aldosterone on transmembrane 22Na efflux from arterial smooth muscle. Rapid and delayed effects.

“…Consequently, it was possible to evaluate the ouabain-dependent (sodium pump) and ouabain-independent fractions of 22 Na efflux. 7 Results are expressed as rate coefficient (min~'), which is calculated by the expression:…”