Abstract
It is important to learn the generating mechanism of the EP, and the distribution of DC potentials in the stria vascularis of the guinea pig cochlea was investigated by inserting a recording microelectrode into the scara media through the stria vascularis.
The microelectrode was driven at 3 microns per second by a special hydraulic autodrive micromanipulator and the position of the electrode tip was identified by the electrophoretic dye-injection (marking method).
Several positive DC steps were always recorded from various parts of the stria vascularis, and the experimental results obtained by marking methods suggested that the source of these positive DC steps was the intracellular potential of the strial cell. The data substantiated that the intracellular potentials of the strial cells are positive, whereas it is common knowledge that the intracellular potential should be negative. In most cases, 3 steps of the positive DC potential could be recorded corresponding to the layers of the strial cells. It must be presumed that the positive DC steps were recorded at the moment of pushing through the strial cell membrane by a recording microelectrode, and the largest 3rd positive step arose from the marginal cell membrane facing the intermediate cell. In the marginal cells, the positivity of the intracellular DC potential reached as high as +80mV, which is still a few millivolts less than the positivity of the EP.
It has been well known that the negative potential is generally recorded from inside the cell, as the membrane is much more permeable to K-ions than to Na-ions are extruded from inside the cell by active sodium ion transport. Suppose that the positive component of the EP is the positive secretion potential generated by the electrogenic potassium ion pump located in the strial cell membrane as having been postulated by Kuijpers, it could be assumed that the strial cell membrane is selectively permeable to Na-ions and not to K-ions. On this assumption, it might be expected that the positive intracellular DC potentials in the strial cells are composed of both the sodium ion concentration gradient between the interior and the exterior of the strial cell and the electrogenic active transport of K-ions in the strial cell membrane.
