Effects of removal of NA⁺ and Cl^- on spontaneous electrical activity, slow wave, in the circular muscle of the guinea-pig gastric antrum

In the circular muscle of the guinea-pig gastric antrum, a decrease in the external Na⁺ to less than 20 mM produced depolarization of the membrane with transient prolongation of the slow wave. This was followed by a high rhythmic activity. The activity was inhibited by reapplication of Na⁺ before recovery. The depolarization in Na⁺-deficient solution was prevented and rhythmic activity continued at about 5/min for at least 6 min by simultaneous removal of K⁺, Ca²⁺, or Cl^-. After exposure to a NA⁺- and Cl^--deficient solution for a few minutes, reapplication of the Na⁺ in Cl^--deficient solution inhibited generation of the slow wave until Cl^- reapplication. Similar results were obtained when Na⁺ and Cl^- were reapplied in the absence of K⁺ after exposure to a Na⁺-, K⁺-free, an Cl^--deficient solution, although the inhibition was weaker than Na⁺ reapplication in a Cl^--deficient solution. In the presence of furosemide or bumetanide, a strong inhibition of activity was produced by the reapplication of Na⁺ and Cl^- after exposure to an Na⁺- and Cl^--deficient solution. A hypothesis is presented that intracellular Ca²⁺ concentration ([Ca²⁺]_i) is the most important factor determining the generation and frequency of the slow wave and that [Ca²⁺]_i is regulated by the Na⁺ concentration gradient across the plasma membrane. The recovery of the Na⁺ concentration gradient by Na⁺ reapplication after removal of Na⁺ and Cl^- is mainly controlled by a Na⁺-K⁺-Cl^- co-transport.