Biology Reference
In-Depth Information
Na
+
Ca
++
Ca
++
Plasma
membrane
Outer
segment
Cytoplasm
Disks
Na
+
Ca
++
Inner
segment
Nucleus
Synaptic
terminal
Fig. 24.3 Schematic diagram of the rod receptor illustrating circulating
current. Only Na
+
and Ca
2+
are shown. Note that the stack of disks
where the photopigment rhodopsin is embedded is separated from the
plasma membrane.
indeed, controlled by an allosteric, positively cooperative protein.
Firstly, Fesenko
et al
. (
1985
) discovered that cGMP, contrary to
previous assumptions, bound directly to the cytoplasmic face of the
ion channels of the plasma membrane of the outer segments of the
photoreceptors and thereby regulated the transmembrane ion flux
cooperatively. Secondly, from nucleotide sequence analysis of cloned
DNA, Kaupp
et al
. (
1988
,
1989
) attempted to identify the primary
structure of the light-sensitive ion channel of the plasma membrane
of the outer segment of the bovine retinal rod photoreceptors, and
found that the functional light channel was an oligomeric protein
