AbstractThe asymmetry of ATP‐reactivated flagellar bending waves of Triton‐demem‐brated sea urchin spermatozoa has been measured over a range of free Ca2+ion concentrations from 10−9to 10−4M. Detailed examination of the gradual response of asymmetry to Ca2+ion concentration over this wide range indicates the presence of two Ca2+sensors. A high‐affinity sensor operates at Ca2+concentrations near 10−7.5M. A lower‐affinity sensor operates at Ca2+concentrations above 10−6M, in the typical range for calmodulin‐mediated responses. Incubation of demembranated sperm flagella at high Ca2+concentrations to release calmodulin is required to enable these Ca2+responses to be observed. This treatment also causes a decrease in the apparent affinity of the flagella for cal‐modulin, as determined by measuring the increase in asymmetry in response to addition of exogenous calmodulin at
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