CALCIUM-DEPENDENT BIDIRECTIONAL POWER STROKE OF THE DYNEIN ARMS IN SEA-URCHIN SPERM AXONEMES

Active sliding between doublet microtubules of sea urchin sperm axonem es that were demembranated with Triton X-100 in the presence or absenc e of calcium was induced with ATP and elastase at various concentratio ns of Ca2+ to examine the effects of Ca2+ on the direction of the powe r stroke of the dynein arms. Dark-held light microscopy of microtubule sliding revealed that the sliding from the axonemes demembranated wit h Triton and millimolar calcium and disintegrated with ATP and elastas e showed various patterns of sliding disintegration, including loops o f doublet microtubules formed near the head or the basal body. These l oops were often thicker than the remaining axonemal bundle. In contras t, only thinner loops were found from the axonemes demembranated with Triton in the absence of calcium and disintegrated with ATP and elasta se at high Ca2+ concentrations. Electron microscopic examination of th e direction of microtubule sliding showed that the doublet microtubule s in the axonemes demembranated in the presence of millimolar calcium moved toward the base of the axonemes by the dynein arms on the adjace nt doublet microtubule as well as by their own dynein arms. Doublet mi crotubules in the axonemes demembranated in the absence of calcium mov ed toward the base of the axonemes only by their own dynein arms, Simi lar observations have been obtained from the axonemes from which the o uter dynein arms were selectively extracted, From these observations, we can conclude that the dynein arms generate force in both directions and this feature of the dynein arms arises from at least the inner dy nein arms.