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

Abstract

Tracer movements and ionic composition were observed in the smooth muscle of the guinea-pig taenia-coli in vitro at 4 and 35[degree] C. The muscle was quiescent at 4[degree] C, and did not show spontaneous electrical or mechanical activity for 25 min. after re-warming. The rate of loss of tracer Na was sensitive to changes of temperature, with an average Q10 of 3.4 [plus or minus] 0.4 on warming in the range 4-35[degree] C. Exponential analysis of Na24 efflux at 35[degree] C showed an initial rapid phase, a 2nd phase with t1/2 =2 min. and a slowly exchanging phase. The 2nd 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[degree]C would then be 30 p-mole cm-2 sec.-1, and 20% of the available metabolic energy would be required to maintain this exchange. The rate of loss of tracer Na was somewhat reduced In K-free or Na-free solutions. The cell size increased at 4[degree] C, and decreased again on warming, while Na and Cl left the cell and K was taken up. The cell chloride content was linearly related to cell size, indicating that the cytoplasm is osmotically isotonic and electrically neutral and that some Na, K and Cl are sequestered elsewhere in the tissue. The quiescent smooth-muscle cell membrane is more permeable to Na than the skeletal-muscle cell membrane.