Figure 1.

Responses of rat mesenteric lymphatics to mibefradil and Ni²⁺. Pressure = 3 cmH₂O. Sample recording showing concentration-dependent effect of mibefradil on the contraction pattern. FREQ begins to slow at concentrations < 1 nM, with further slowing at concentrations up to 50 nM. At 200 nM, all activity ceased following a single contraction. (B) Summary of effects of mibefradil on AMP, showing tendency of AMP to rise at low mibefradil concentrations (also evident in A) before declining at concentrations > 50 nM. (C) Summary showing concentration-dependent inhibition of FREQ by mibefradil. The IC₅₀ for FREQ was substantially lower than that for AMP, suggesting a selective inhibition of FREQ at low concentrations. (D) Sample recording showing concentration-dependent inhibition by Ni²⁺ of both AMP and FREQ of rat mesenteric lymphatics. (E,F) Summary of effects of Ni²⁺ on AMP (E) and FREQ (F). FREQ inhibition was biphasic, with partial inhibition at low concentrations, partial recovery at intermediate concentrations, followed by full inhibition at concentrations > 200 μM. The data in F could not be fit to the Hill equation and so the curve was interpolated and used to estimate an IC₅₀ = 287 μM.