In the preceding article, we investigated the spatial properties of the induction of the prolonged depolarizing afterpotential (PDA) by shifting visual pigment from the rhodopsin (R) to the metarhodopsin (M) state in the barnacle photoreceptor. In this work, we have studied the ranges within the cell of the antagonistic effects on the PDA of M-to-R transfer. When this transfer occurs during a PDA, it depresses the PDA; when it precedes PDA induction, it impedes that induction ("anti-PDA"). These ranges were previously shown (by a statistical technique) to be at least a few tens of nanometers within a half-second (D greater than 10(-13) cm2 s-1). We now demonstrate, with local illumination techniques in which a PDA was induced in one side of the cell and PDA depression or anti-PDA was induced in the other side, that both ranges are much smaller than the cell diameter (approximately 100 microns) within 30 s (D less than 10(-6)). We further show, using a less direct but shorter-range technique involving colored polarized light, that the interaction of the PDA with the anti-PDA is restricted to less than approximately 6 microns (D less than 6 X 10(-9)). This figure is quite low and suggests that the interaction may be confined to the pigment molecules, possibly in a complex of the type suggested in the preceding article.

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