The cross-bridge mechanism studied by flash photolysis of caged ATP in skeletal muscle fibers.

Flash photolysis of caged ATP was first employed in muscle cell physiology about 15 years ago. This technique enables examination of the millisecond dynamics of synchronized cross-bridge ATPases in muscle fibers, and consequently, many photolysis studies have been performed in attempt to elucidate the cross-bridge mechanism. The results of early studies with caged ATP seemed to support the classical "power stroke" theory. However, much of the recent evidence indicates that the contraction induced by the photolysis of caged ATP differs from that predicted by the classical theory. One elusive problem is the biphasic tension development that occurs on the photorelease of ATP in the ADP-rigor fiber in the presence of Ca2+. Another is the long-lasting burst of Pi release after the release of ATP. Further investigations are required to clarify the chemo-morpho-mechanical coupling involved in the cross-bridge reaction.