The distribution of ions in the smooth muscle of the guinea‐pig taenia coli

Abstract

SUMMARY1. Tracer movements and ionic composition have been observed in the smooth muscle of the guinea-pig taenia coil in vitro at 4, and 350 C. The muscle was quiescent at 40 C, and did not show spontaneous electrical nor mechanical activity for 25 min after re-warming. It was therefore possible to make observations on the quiescent tissue at 350 C.2. The rate of loss of tracer sodium was sensitive to changes of temperature, with an average Qlo of 3-4 + 0-4 on warming in the range 4-350 C.Exponential analysis of 24Na efflux at 35°C showed an initial rapid phase, a second phase with ti = 2 min, and a slowly exchanging phase. The second phase was most sensitive to changes of temperature and contained 15 m-mole Na/kg fresh wt. The corresponding transmembrane flux in spontaneously active muscle at 35°C would then be 30 p-mole cm-2 sec-', and 20 % of the available metabolic energy would be needed to maintain this exchange. 3. The rate of loss of tracer sodium was reduced in potassium-free or sodium-free solutions, but the effects were not impressive.4. The cell size increased at 40 C, and fell again on warming while Na and Cl left the cell and K was taken up. Cell chloride content was linearly related to cell size.5. The observations are interpreted on the assumption that the cytoplasm is osmotically isotonic and electrically neutral, and that some Na, K and Cl are sequestered elsewhere in the tissue. It is concluded that the quiescent smooth-muscle cell membrane is rather more permeable to sodium than the skeletal-muscle cell membrane.

The Action of Adrenaline on the Ionic Content and on Sodium and Potassium Movements in the Smooth Muscle of the Guinea‐pig Taenia Coli

“…Figure la shows the same results as in Fig. la present in the slow phase (Buck & Goodford, 1966 (Goodford, 1962). It was found that adrenaline again increased the loss of 24Na significantly.…”

“…4) instead of the curve normally found. It has been suggested that the curvature normally observed is due to an inhomogeneous distribution of potassium in the tissue (Goodford & Hermansen, 1961;Bauer et al, 1963;Buck & Goodford, 1966), and the present observations might indicate that more of the tissue potassium is exchangeable in the presence of adrenaline than under control conditions. They might alternatively be due to a changed ratio of cell volume to cell surface area, as has previously been observed by Freeman-Narrod & Goodford (1962).…”

“…In order to test the action of adrenaline on the coupled Na-K pump, it was applied to the taenia at the moment when the temperature was raised from 40 to 250 C. According to Buck & Goodford (1966), this increase of temperature stimulates the active extrusion of Na and the uptake of K, but not maximally, since a further increase would be possible if the temperature were raised still higher. It was found that adrenaline had no effect under these conditions, and it must be concluded that it has no effect on active ion transport during recovery from cooling.…”

Effects of thymol on the electrical and mechanical properties of the guinea‐pig taenia coli

“…This result might suggest that the determination of the membrane potential is independent of Cl permeability. It has often been assumed that C1 in smooth muscle of the taenia col is distributed passively across the cell membrane (Buck & Goodford, 1966). On the other hand, some evidence against a passive distribution of Cl has been proposed (Casteels & Kuriyama, 1966;Casteels, 1969Casteels, , 1971.…”

Proceedings of the Physiological Society, 10‐11 November 1967, Mill Hill Meeting: Communications

“…The low cytoplasmic concentration of sodium (37.5 mM, Buck & Goodford, 1966) would therefore be at equilibrium across the curved vesicular surface with some 900 mM-Na, which exceeds the extracellular concentration of 137 mM-Na. Since many vesicles are observed to have openings into the extracellular fluid, the sodium might finally escape from the cells by this route.…”