Ionic mechanism of ouabain-induced swelling of leech Retzius neurons.

By using electrophysiological and microfluorimetric methods, we found that leech Retzius neurons swell after inhibition of the Na(+)-K(+) pump by the cardiac glycoside ouabain. To explore the mechanism of this swelling, we measured the effect of ouabain on Na(+), K(+), and Cl(-), as well as on the membrane potential, by applying triple-barrelled ion-sensitive microelectrodes. As shown previously, ouabain induced a marked Na(+) increase, a K(+) decrease, and a membrane depolarization, and it also evoked an increase in Cl(-). The analysis of the data revealed a net uptake of NaCl, which quantitatively explained the ouabain-induced cell swelling. In the absence of extracellular Na(+) or Cl(-), NaCl uptake was excluded, and the cell volume remained unaffected. Likewise, NaCl uptake and, hence, cell swelling did not occur when the Na(+)-K(+) pump was inhibited by omitting bath K(+). Also, in K(+)-free solution, Na(+) increased and K(+) dropped, but Cl(-) slightly decreased, and after an initial, small membrane depolarization, the cells hyperpolarized for a prolonged period. It is concluded that the ouabain-induced NaCl uptake is caused by the depolarization of the plasma membrane, which augments the inwardly directed electrochemical Cl(-) gradient.