Abstract.
Chronic KCl-induced depolarization of Paramecium tetraurelia enhances Ca2+-dependent backward swimming behavior over a period of 8–24 hr. Here, we investigated the electrophysiological mechanisms underlying this adaptive phenomenon using voltage-clamp techniques. Cells that had been adapted to 20 mm KCl showed several significant changes in the properties of the Ca2+ current that mediates ciliary reversal in Paramecium (I Ca ), including a positive shift in voltage sensitivity and a significant slowing of inactivation. In seeking an explanation for these changes, we examined the effects of chronic depolarization on mutants that do not normally express a Ca2+ current or swim backward. Surprisingly, pawn B mutant cells slowly regained the ability to reverse their cilia during KCl exposure with a time course that mirrored behavioral adaptation of the wild type. This behavior was accompanied by expression of a novel Ca2+ current (I QUEEN ) whose voltage sensitivity was shifted positive with respect to the wild-type Ca2+ current and that was slow to inactivate. Coincidental expression of I QUEEN in the wild type during adaptation would readily explain the observed changes in I Ca kinetics. We also examined the effects of chronic depolarization on Dancer, a mutant suggested previously to have an I Ca inactivation defect. The mutant phenotype could be suppressed or exaggerated greatly by manipulating extracellular KCl concentration, suggesting that Dancer lesion instead causes inappropriate regulation of I QUEEN .
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Received: 23 April 1999/Revised: 29 June 1999
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Preston, R., Hammond, J. Ca2+ Current-Deficient Pawn Mutants are Promoted to Queens During Chronic Depolarization of Paramecium tetraurelia . J. Membrane Biol. 171, 245–253 (1999). https://doi.org/10.1007/s002329900575
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DOI: https://doi.org/10.1007/s002329900575