The Journal of Cell Biology, Vol 77, 19-R26, Copyright © 1978 by The Rockefeller University Press
Cation-induced attachment of ciliary dynein cross-bridges
F. D. Warner
Isolated, demembranated Unio gill cilia that have been activated and fixed
for thin-section electron microscopy in the presence of 2 mM MgSO4 have 87%
of their outer dynein arms attached to an adjacent B subfiber. The
distribution of attached arms is uniform with respect to doublet position
in the cilium. When both 0.1 mM ATP and Mg++ are added to the activation
and fixation solutions, the frequency of bridged arms is reduced to 48%. At
the same time, the distribution of the attached arms appears to have been
systematically modified with respect to doublet position and the active
bend plane. Those doublet pairs positioned in the bend plane where
interdoublet sliding is minimal retain a greater number of bridged arms
than those doublet pairs positioned outside the bend plane where sliding is
maximal. These observations imply a functional coupling of the Mg++-induced
bridging of the dynein arms and the subsequent binding and hydrolysis of
ATP that results in a force-generating cross-bridge cycle.
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