Electrical impedance, ultrastructure and ion transport in foetal gastric mucosa.

1. The voltage transient developed across rabbit foetal gastric mucosa in response to rectangular current pulses was measured under in vitro conditions. The short-circuit current was also measured.2. The voltage transients were used to calculate equivalent circuit parameters. The mucosa could be represented as two large capacitances in series, each shunted by a high conductance.3. Electron microscopy was carried out on some preparations after the electrical measurements had been made. An extensive smooth membrane tubular system was observed on the apical sides of the cells, with openings into the gastric lumen.4. Anoxia resulted in a reversible reduction in value of the large capacitance and short-circuit current: the relative changes in these two quantities were very closely linked. Electron microscopy showed a large and reversible decline in the extent of the apical tubular system during anoxia.5. It was concluded that the apical tubular system plays an important role in ion transport in this preparation. Considerations of the magnitude of the capacitances and of membrane area suggest that the smaller capacitor represents the plasma membrane. The dieletric constant of the smooth membrane of the tubular system is an order of magnitude lower than that of the plasma membrane.