An interaction between potassium and sodium in the smooth muscle of the guinea-pig taenia coli

摘要

1. The potassium content of the guinea-pig taenia coli was 72 m-mole K/kg fr. wt. after equilibration with normal Krebs-type solution at 35° C in vitro.2. It fell to 13 m-mole K/kg fr. wt. when Ca²⁺ and Mg²⁺ were omitted from the bathing solution, but this fall was reversed in part when [Na⁺]o was also reduced.3. The taeniae relaxed when Ca²⁺ and Mg²⁺ were omitted from the normal solution. However, they contracted if Na⁺ was also omitted.4. Effects 2 and 3 may show some antagonism between sodium and divalent cations in smooth muscle.5. The extracellular space of the same muscles was measured with [¹⁴C]sorbitol. It was 440 ml./kg fr. wt. in normal solution.6. The uptake of ⁴²K was measured in the same muscles at the same time. An initial rapid exchange was followed within 2 min by a slow (half-time [unk] 50 min in normal solution) and presumably intracellular uptake of tracer.7. In normal solution the initial rapid phase of ⁴²K exchange corresponded to 3·0 m-mole K/kg fr. wt. A value of 2·6 m-mole K/kg fr. wt. would have been calculated from [K⁺]o and the [¹⁴C]sorbitol space, and these estimates did not differ significantly.8. The [¹⁴C]sorbitol space fell slightly when [Ca²⁺]o, [Mg²⁺]o, and [Na⁺]o were reduced, but the amount of rapidly exchanging potassium increased significantly reaching 4·6 m-mole K/kg fr. wt. in solutions from which Ca²⁺, Mg²⁺ and Na⁺ were omitted. The [¹⁴C]sorbitol space only accounted for 2·4 m-mole K/kg fr. wt. under these conditions, a significantly smaller quantity.9. The observations have been interpreted on Wilbrandt & Koller's (1948) hypothesis that there may be a superficial anionic region in muscle cells. On this model the present results suggest that K⁺ rather than Na⁺ is favoured as a monovalent counter-cation in the taenia coli.