State and distribution of potassium and sodium ions in frog skeletal muscle

313

219

SUMMARY1. The intracellular Na activity of sheep heart Purkinje fibres has been measured using recessed-tip Na+-sensitive glass micro-electrodes.2. The internal Na activity was 7-2 + 2-0 mm (mean + S.D., n = 32) at the normal external Na concentration, [Na]0, in these experiments of 140 mm (equivalent to an external Na activity of 105 mM). The equilibrium potential for Na across the fibre membrane was therefore approximately + 70 mV. 4. The removal of external K produced an easily reversible increase in the internal Na with an initial rate equivalent to a concentration change of 0-24 + 0 07 m-mole/min (mean + S.D., n = 8).5. Ouabain produced increases in the internal Na activity that were only very slowly reversible. The threshold concentration for producing an increase was approximately 10-7 M. 10. The relationship between internal Na and contractility is discussed.

Section: Discussionmentioning

confidence: 99%

The effects of external cations and ouabain on the intracellular sodium activity of sheep heart Purkinje fibres

Ellis¹

1977

313

219

“…A bicompartmental arrangement of Na+ seems to exist also in skeletal muscle. It is interesting to comment in particular on the measurements of intracellular Na+ activity determined with ion sensitive micro-electrodes in frog skeletal muscle by Lee & Armstrong (1974).…”

Section: Discussionmentioning

confidence: 99%

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

Garay

Moura

Osborne-Pellegrin

et al. 1979

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.

“…For example, Na+ activity coefficients of 0-20 (Lev, 1964) -027 (Lee & Armstrong, 1974), and K+ activity coefficients of 0-66-0 69 (Lee & Armstrong, 1974) (1984), are needed to determine unambiguously the size of the bound pools.…”

Section: Microprobe Anal Ysis Of Cell Fluid Restricted Elements In Frmentioning

confidence: 99%

Diffusible sodium, potassium, magnesium, calcium and phosphorus in frog skeletal muscle.

Maughan¹,

Recchia²

1985

SUMMARY1. A microvolumetric analytical method has been developed to measure the endogenous concentrations of diffusible elements in muscle cells.2. Single twitch fibres from frog muscle were skinned under oil and 0-2 nl drops of isosmotic sucrose solution, held in the tips of specially constructed pipettes, were placed in contact with the skinned fibres. After 0-10 min, the microdrops were removed and analysed with a wave-length dispersive X-ray spectrometer.3. The uptake of Na, K, Mg, and P into the microdrops was well fitted by a single exponential function, while the uptake of Ca was better represented by the sum of two exponential functions. All elements analysed except Ca reached diffusional equilibrium within 5 min of placing the microdrop on the fibre, while Ca was still not equilibrated at 10 min.4. For freshly isolated muscle fibres, diffusible element concentrations in the microdrops at equilibrium were (in mm, mean + S.D.): Na, 7-6 ± 72; K, 82 + 36; Mg, 5-8 + 30; P, 51+19. Diffusible Ca concentration (at 10 min elapsed sampling time) was 0-7+04 mM.5. Results from experiments in which microdrops were equilibrated with skinned fibres pre-soaked in an artificial (Ca-free) solution support the notion that the exogenous solutes can replace the endogenous diffusible contents of a skinned fibre by soaking the skinned fibre in a relatively large volume of the artificial solution.6. Total Na, K, Mg, Ca, and P content of whole muscle was measured by electron probe analysis of muscle extracts. In freshly isolated muscle, whole muscle element content was (in mmol/kg wet weight, mean + S.D.): Na, 21+8; K, 120+ 26; Mg, 9-7+2-6; Ca, 2-2+0-5; P, 76+ 18.