Abstract
Trichocyst discharge, ciliary reversal, and cell body contraction inParamecium spp. have all been claimed to be regulated by the intracellular Ca2+ concentration ([Ca2+]i) at the cortical region of the cell. We injected caged Ca2+ intoP. caudatum cells and applied ultraviolet (UV) light to the cell for 125 ms. This did not induce trichocyst discharge but did induce both ciliary reversal and cell body contraction. A re-application of UV for 125 ms triggered trichocyst discharge. These results demonstrate that (1) trichocyst discharge and ciliary reversal and cell body contraction are controlled by [Ca2+]i and (2) the threshold of [Ca2+]i for trichocyst discharge is higher than those for the other two functions.
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