AJP - Cell Physiology, Vol 254, Issue 1 C27-C36, Copyright © 1988 by American Physiological Society
[ATP]i in Limulus photoreceptors: no correlation with responsiveness or discrete event rate
L. J. Rubin and J. E. Brown
Department of Ophthalmology, Washington University School of Medicine, St. Louis, Missouri 63110.
Firefly luciferin-luciferase was microinjected into single, intact
photoreceptor cells of Limulus ventral eyes. In addition, total ATP content
of whole end organs was measured. An attempt was made to correlate
intracellular ATP levels with either the frequency of discrete events or
responsiveness to light. Luciferin-luciferase luminescence emitted from a
single photoreceptor cell increased after an injection of ATP or P[NH]P and
decreased after injection of apyrase. We conclude that the
luciferin-luciferase luminescence is monitoring increases as well as
decreases in intracellular ATP concentration (ATPi). The ATPi was between
10(-3) and 10(-4) M. Bathing ventral eyes in vanadate or fluoride increased
ATP content of whole end organs, increased ATPi in single photoreceptors,
and increased the frequency of discrete events. However, apyrase decreased
ATPi but did not affect the frequency of discrete events or responsiveness
to light until ATPi was dramatically reduced. We conclude that changes in
ATP levels are not strictly correlated with changes in responsiveness to
light or to changes in the frequency of discrete events.
