Membrane potential and ion content in the smooth muscle of the guinea‐pig's taenia coli at different external potassium concentrations

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Abstract
The relation between the membrane potential and the intracellular ion concentration of the taenia-coli was studied in solutions with different external K concentrations. Isotonic solution in which the sum of NaCl + KCl was constant did not produce swelling of the smooth muscle of taenia-coli even at high [K]o, and did not change the intracellular chloride concentration. Addition of an equivalent amount (118 mM) of NaCl or KCl to Krebs solution produced the same loss of water. Solutions In which the product [X] [Cl] was kept constant decreased the internal chloride concentration so that the chloride equilibrium potential became temporarily positive and returned only after 2 hr. to a negative value. The chloride ions are probably not passively distributed as indicated by these results and that the ECl was about 35 mV more positive than the membrane potential even in normal Krebs solution. The K equilibrium potential is the main factor in the generation of the membrane potential. The large discrepancy between the 2 is probably due to the non-passive chloride distribution and the Na permeability of the membrane. The maintenance of the normal cell volume in solutions with constant sum of NaCl + KCl is explained by the constant intracellular chloride concentration.