Effect of potassium on membrane potential and tension development in bovine mesenteric lymphatics

Abstract

The transmembrane potential and tension of the smooth muscle of isolated bovine mesenteric lymphatics were recorded in solutions having various potassium concentrations. The relation between the membrane potential and the logarithm of the external K + concentration was observed. The maximum slope was 39 mV per 10-fold change in [K +] 0. The minimum depolarization necessary for inducing contraction was 6 mV. The maximal contraction was recorded at a [K +] 0 of 60 m M. In K-free solution, the membrane depolarized by about 9 mV, and the muscle developed a sustained tension. The addition of 10 −5 M ouabain to normal Krebs solution caused a depolarization of the membrane and a sustained contraction. The depolarization and tension development in the K-free solution were potentiated by 10 −5 M ouabain. These observations suggest that changes of membrane potential may play a major role in the activation of the contractile protein in lymphatic smooth muscle and also that there is an electrogenic sodium pump in the membrane. The depolarization and tension development in K-free solution may be due to a decreased activity of the electrogenic Na pump.