CAMP‐mediated inhibitory effect of calmodulin antagonists on ciliary reversal of Paramecium

Abstract

AbstractTo explore possible roles of calmodulin in Ca2+‐induced ciliary reversal, we tested the effects of calmodulin antagonists on Triton‐extracted models of Paramecium. In the extracted models prepared by the method of Naitoh and Kaneko [Science 176:523–524, 1972], the Ca2+ ‐induced ciliary reversal was not inhibited by calmodulin antagonists, trifluoperazine (TFP), or 5‐chloro‐l‐naphthalenesulphone amide (W‐7). However, in the presence of adenosine 3′,5′‐cyclic mono‐phosphate (cAMP), whose concentration is below the one that alters the ciliary direction, TFP inhibited ciliary reversal and the models swam forward at 10−5 M Ca2+. When the washing medium in the preparation of the extracted models was replaced with one containing MgCl2, the extracted model showed sensitivity to calmodulin antagonists without addition of cAMP; at 10−5 M Ca2+, 40 μM TFP or 100 μM W‐7 inhibited the ciliary reversal and the models swam forward. Such effect of antagonists was abolished by an inhibitor of cAMP‐dependent protein kinase. On the other hand, addition of cAMP enhanced the inhibitory effect of antagonists. These results suggest that calmodulin antagonists act to increase the extent of cAMP‐dependent protein phosphorylation that inhibits the Ca2+ ‐induced ciliary reversal.