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Active Transport of Potassium by the Cecropia Midgut : VI. Microelectrode Potential Profile
1 Department of Zoology, University of Massachusetts, Amherst, Massachusetts; Department of Zoology, University of Cambridge, England
2 Department of Zoology, University of Massachusetts, Amherst, Massachusetts; Grass Instrument Co., Quincy, Massachusetts
3 Department of Zoology, University of Massachusetts, Amherst, Massachusetts
1. The potential profile recorded as a microelectrode is advanced from the blood side through the isolated midgut of Hyalophora cecropia consists of negative plateaus followed by a large positive step to the full midgut potential.
2. Oxygen deprivation diminishes both the positive step and the midgut potential; the negative plateaus are not affected.
3. Changes in the potassium concentration in the blood-side solution affect both the negative plateaus and the midgut potential; the large positive step remains about the same.
4. From these results it is concluded that the positive step is probably produced by the electrogenic potassium pump and that the negative steps are due to a potassium equilibrium potential.
5. The discrete and independent nature of the negative and positive potentials argues that there are two barriers separating a ‘midgut’ compartment from the two bathing solutions.
6. It is inferred that the epithelial cells are the site of the profile negativity and therefore that they constitute the ‘midgut’ compartment. This interpretation implies that the potassium equilibrium potential appears across the basal cell membranes and that electrogenic pump potential appears across the apical plasma membranes of the epithelial cells.
7. The most conservative interpretation of these results is that the electrogenic potassium pump is located somewhere in or on the apical plasma membrane of the epithelial cells.
Submitted on June 17, 1968
