Calcium sensors in sea urchin sperm flagella.
The asymmetry of ATP-reactivated flagellar bending waves of Triton-demembrated sea urchin spermatozoa has been measured over a range of free Ca2+ ion concentrations from 10(-9) to 10(-4) M. 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(-7.5) M. A lower-affinity sensor operates at Ca2+ concentrations above 10(-6) M, 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 calmodulin, as determined by measuring the increase in asymmetry in response to addition of exogenous calmodulin at low Ca2+ concentration.
Brokaw
C J
CJ
Division of Biology, California Institute of Technology, Pasadena 91125.
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002147:Calmodulin / Q000502:physiology*; D008297:Male; D012617:Sea Urchins; D013081:Sperm Motility / Q000502:physiology; D013082:Sperm Tail / Q000502:physiology*
D002147:Calmodulin; D002118:Calcium