In order to clarify whether or not the electronegative olfactory mucosal potentials (EOG) are generator potentials, the effects of changed ionic enviroment were studied. The EOG decreased in amplitude and in some cases nearly or completely disappeared, when Na+ in the bathing Ringer solution was replaced by sucrose, Li+, choline+, tetraethylammonium+ (TEA), or hydrazine. In the K+-free Ringer solution, the negative EOG's initially increased and then decreased in amplitude. In Ringer's solution with increased K+, the negative EOG's increased in amplitude. When K+ was increased in exchange for Na+ in Ringer's solution, the negative EOG's decreased, disappeared, and then reversed their polarity (Fig. 6). Next, when the K+ was replaced by equimolar sucrose, Li+, choline+, TEA+, hydrazine, or Na+, the reversed potentials recovered completely only in Na+-Ringer's solution, but never in the other solutions. Thus, the essential role of Na+ and K+ in the negative EOG's was demonstrated. Ba++ was found to depress selectively the electropositive EOG, but it hardly decreased and never increased the negative EOG. Hence, it is concluded that Ba++ interferes only with Cl- influx, and that the negative EOG's are elicited by an increase in permeability of the olfactory receptive membrane to Na+ and K+, but not to Cl-. From the ionic mechanism it is inferred that the negative EOG's are in most cases composites of generator and positive potentials.

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