Regulations of Microtubule Sliding by Ca²⁺ and cAMP and Their Roles in Forming Flagellar Waveforms

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The function of Ca²⁺ and cAMP in extruding doublet microtubules from sea urchin sperm axoneme and generating flagellar waves was investigated in order to clarify the regulatory mechanism of microtubule sliding and the formation mechanism of beating patterns of cilia and flagella. Almost all potentially asymmetric spermatozoa that were demembranated with Triton in the absence of Ca²⁺ and reactivated with MgATP²⁻ (Gibbons, B.H. and Gibbons, I.R. (1980). J. Cell Biol., 84: 13–27), beat with planar waves closely resembling those of the intact spermatozoa, whereas potentially symmetric spermatozoa, in which axonemal calmodulin was removed by detergent extraction in the presence of millimolar Ca²⁺ (Brokaw, C.J. and Nagayama, S.M. (1985). J. Cell Biol., 100: 1875–1883), beat with three-dimensional waves if they were reactivated with low MgATP²⁻. At a high MgATP²⁻, almost all demembranated spermatozoa beat with planar waves. cAMP enhanced the three-dimensionality of the flagellar waves at a low Ca²⁺. These changes in the flagellar waves were caused by different regulations of the microtubule sliding by calcium, cAMP, and MgATP²⁻.