Internal calcium concentration and potassium permeability in Paramecium

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Abstract
Ca or EGTA was ionophoretically injected into Paramecium tetraurelia to change [Ca]1. Ca decreased the resting membrane resistance and hyperpolarized the membrane. EGTA had the opposite effect. EGTA following TEA, which suppress GK, had little effect on resistance or resting potential. The I—V relation at steady state was studied before and after EGTA injection while the cell bathed in either K‐ or TEA‐solution. The response to inward test pulses after EGTA injection was similar to that after TEA injection. These results show that [Ca]i controls a steady‐state K permeability in Paramecium tetraurelia. A prolonged Ca‐spike was recorded after EGTA injection. The plateau potentials in various Ca concentrations in a TEA‐solution show the Nernst slope (29 mV for tenfold change in [Ca]0). This result suggests that the prolonged depolarization in this condition is due to a Ca current, after suppression of K‐permeability and when [Ca]i is low. The difficulty of obtaining quantitative data an the internal Ca, and the difference between the effects of EGTA injection and TEA injection are discussed.