J Biol Chem, Vol. 273, Issue 33, 20795-20801, August 14, 1998
Evidence for the Involvement of Inositol Trisphosphate but Not
Cyclic Nucleotides in Visual Transduction in Hermissenda
Eye
Manabu
Sakakibara
,
Hiroko
Inoue¶, and
Tohru
Yoshioka¶
From the
Department of Biological Science and
Technology, School of High Technology for Human Welfare, Tokai
University, Numazu 410-03, Japan and the ¶ Department of Molecular
Neurobiology, School of Human Sciences, Waseda University,
Tokorozawa 359, Japan
Although several second messengers are known to
be involved in invertebrate photoresponses, the mechanism underlying
invertebrate phototransduction remains unclear. In the present study,
brief injection of inositol trisphosphate into Hermissenda
photoreceptors induced a transient Na+ current followed by
burst activity, which accurately reproduced the native photoresponse.
Injection of Ca2+ did not induce a significant change in
the membrane potential but potentiated the native photoresponse.
Injection of a Ca2+ chelator decreased the response
amplitude and increased the response latency. Injection of cGMP induced
a Ca2+-dependent, transient depolarization with
a short latency. cAMP injection evoked
Na+-dependent action potentials without a rise
in membrane potential. Taken together, these results suggest that
phototransduction in Hermissenda is mediated by
Na+ channels that are directly activated by inositol
trisphosphate without mobilization of cytosolic Ca2+.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.