Abstract
Effects of some chemicals, which are known as inhibitors of Ca2+-dependent ATPases, on the water receptor of the frog tongue were examined by using single fungiform papilla preparations. When a sufficient amount of ruthenium red, quinacrine hydrochloride, ethacrynic acid or 2, 4-dinitrophenol was added to the standard stimulating solution.(5mM CaCl2+100mM NaCl), which has been shown to stimulate sufficiently the water receptor of the frog tongue, no neural response was elicited. The concentrations necessary for 50% inhibition were approximately 3×10-6M for ruthenium red, 1×10-5M for quinacrine hydrochloride, 1×10-3M for ethacrynic acid and 2×10-4M for 2, 4-dinitrophenol. Organic mercurials, mersalyl acid and p-chloromercuribenzoic acid, had no effect on the neural response, but repeated application of these chemicals led to a permanent depression in receptor activity. Ouabain had no effect on either the neural response or receptor activity. These observations indicate that the receptor molecule of the frog water receptor has a similar property to that of the Ca2+-dependent ATPase of red-cell membrane in respect to the susceptibility to inhibitors.
