Differential effects of Quin-2 and Quin 2-AM on ciliary responses of Paramecium caudatum at moderate calcium levels

Abstract

Paramecium cells were suspended in a pH 7.1 buffered solution containing various levels of total CaCl2 (3.9 to 250 μM), Quin-2 or Quin 2-AM and in the absence or presence of various concentrations of KCl, NaCl or BaCl(2). At lower calcium levels especially, Quin-2 behaved as a potent antagonist of KCl-induced continuous ciliary reversal (50% inhibition at 4 μM) and, at higher concentrations, reduced the duration of periodic ciliary reversal responses to NaCl and BaCl(2). The efficacy of Quin-2 as an antagonist of KCl-induced ciliary reversal was reduced by elevation in extracellular calcium. Quin 2-AM, in contrast, slightly increased the duration of continuous ciliary reversal behaviors to KCl and also, in a time-dependent fashion, increased the duration of the recovery time of the cells from KCl stimulation. The results clearly indicate that any use of these indicators to measure changes in ionized calcium in this cell following cation stimulation should be limited to studies at high extracellular calcium levels - concentrations where the cells' responses to cationic stimulation are markedly attenuated.