Inhibitory effects of cations on the Ca2+ response of water fibers in the frog tongue.

The effects of various cations on water fibers in the frog (Rana catesbeiana) tongue were investigated. The following results were obtained. 1. Water fibers responded well to Ca2+ and Sr2+. 2. SO2-(4) did not inhibit the Ca2+ response. Cl- at high concentrations had an inhibitory effect on the response to high Ca2+ stimulation. However, when the Ca2+ concentration was low, Cl- did not induce any inhibition. Therefore, low Ca2+ stimulation (0.1 mM CaCl2) was used to examine the inhibitory effect of cation. 3. MgCl2 and MgSO4 strongly inhibited the response to low Ca2+ stimulation. The inhibition by Mg salts was not caused by anion but by Mg2+. 4. The Ca2+ response was inhibited by various cations. The order of the inhibitory effects of cations was as follows: La3+ greater than Mn2+ = Mg2+ greater than or equal to Ni2+ greater than Co2+ greater than monovalent cations (Na+, K+, NH4+ and choline+). 5. The Sr2+ response, as well as the Ca2+ response, was inhibited by Na+ and Mg2+.