The influence of Ca2+ on the action potential in mesophyll cells ofDionaea muscipula Ellis

Ion fluxes during the action potentials of different characean cells are intensively studied revealing complicated fluxes of both C1and Ca 2+ during depolarisation (for review see BEILBY 1984). In Aldrovanda vesiculosa a strict dependence of the action potential peak depolarisation upon Ca 2+ was found (IIJ~MA and SmAOKA 1985). In the closely related species Dionaea muscipula the situation was not clear since in earlier experiments (JAcoBsoN 1974) only small effects of external ions on the action potential of the sensory cells could be demonstrated. We measured the influence of different ions on the action potential of Dionaea muscipula by impaling microelectrodes into mesophyll cells of small leaf stripes which carried a trigger hair (Fig. 1). Excitation was elicited by bending the hair. The preparation was kept under constant perfusion; ions were tested in concentrations from 0.1 mM to 30 mM under isoosmotic conditions. Solutions were adjusted to pH7 by 3 mM Tris-maleic acid buffer. K + and Na + shift the depolarisation peak by less than 5 mV per tenfold increase in concentration towards a