Analysis of the delayed outward current when substituting Ba++ for Ca++ in Helix pomatia neurons

The present research is concerned with the study of the ionic currents in some neurons of the Helix pomatia subesophageal ganglia when Ca is replaced by Ba. The cells were impaled with two microelectrodes and voltage-clamped by means of a conventional type electronic circuit. The replacement of the external Ca with an equimolar concentration of Ba resulted in a decrease of the total delayed outward current as the membrane potential was made more positive. The action of barium was voltage dependent. The net outward current during repeated voltage-clamp pulses has been studied too. Responses to repetitive activation with 100 ms repolarization interval were recorded to analyze the deficit in net outward charge transfer under voltage-clamp. In normal saline this deficit in net charge transfer has been related to the inward flow of Ca ions occurring at high depolarizations and obscured by the outward current of potassium. Divalent cation Ba++ produced a reversible depression of delayed outward current and it seems that both the voltage-dependent and Ca-dependent components of the delayed K+ current are affected by this ion.