The appearance of cGMP-gated cation channel protein
in the postnatal rat retina has been studied by fluorescence
immunocytochemistry of radial retinal sections and immunoblots
of retinal membrane proteins. Channel immunoreactivity
was first detectable with RCNGC1-7H2 monoclonal antibody
at postnatal day 7 (PN7) by both methods. Immunocytochemical
label in retinal sections was localized to the outer segments,
and immunoreactivity increased with increasing age. We
also compared the developmental appearance of the cGMP-gated
cation channel to that of other phototransduction proteins
and developmental markers. RET-P2, a monoclonal antibody
recognizing the 39-kDa rds/peripherin disc protein, first
labeled outer segments at PN7, coincident with cGMP-gated
cation channel expression. Double labeling of the same
section of PN7 rat retina with RET-P2 and R309 (a polyclonal
antiserum against the rod cGMP-gated cation channel) revealed
identical patterns of labelling. Similarly, double labeling
with RCNGC1-7H2 and an antibody against the rod cGMP-phosphodiesterase
gave coincident labeling, suggesting coordinate expression
mechanisms of phototransduction proteins with each other
and with outer segment structural proteins.