Properties of the slow inward current induced by pentylenetetrazol in Helix neurons.

The slow inward current (SIC) induced by 50 mM pentylenetetrazol was studied on central neurons of Helix pomatia in view of its ionic dependence and sensitivity to channel blockers in the presence of 30 mM TEA. A single electrode voltage clamp was used to measure currents evoked by ramp pulses and voltage steps. Sodium withdrawal had variable effects on this current while TTX had no influence on it. Inorganic and organic calcium channel blockers, on the contrary, always produced a partial or total block of the SIC. It is concluded that the slow inward current is mediated by Ca channels impaired by PTZ. Various ions--Na, Ca, and even Tris--may participate in it in variable proportions.