Inhibitory Effects of Cations on the Ca2+ Response of Water Fibers in the Frog Tongue

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Abstract
The effects of various cations on water fibers in the frog (Rana catesbeiana) tongue were investigated. Water fibers responded well to Ca2+ and Sr2+ while .**GRAPHIC**. did not inhibit the Ca2+ response. Cl- at high concentrations had an inhibitory effect on the response to high Ca2+ stimulation, but when the Ca2+ concentration was low, Cl- did not induce any inhibition. Low Ca2+ stimulation (0.1 mM CaCl2) was used to examine the inhibitory effect of cation. MgCl2 and MgSO4 strongly inhibited the response to low Ca2+ stimulation; the inhibition by Mg salts was not caused by anion but apparently by Mg2+. The Ca2+ response was inhibited by various cations. The order of the inhibitory effects of cations was as follows: La3+ > Mn2+ = Mg2+ .gtoreq. Ni2+ > Co2+ > monovalent cations (Na+, K+, NH+ and choline+). The Sr2+ response, as well as the Ca2+ response, was inhibited by Na+ and Mg2+.