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 .
The Journal of Membrane Biology – Springer Journals
Published: Oct 1, 1999
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