[H-3]Quinuclidinyl benzylate (H-3-QNB) specific binding of the develop
ing rat retinal pigment epithelium (RPE) and neural retina has been ex
amined. The binding of H-3-QNB to RPE was saturable and displaced by t
he antagonist pirenzepine. Scatchard analysis of H-3-QNB binding showe
d two high affinity sites to RPE, with K-B = 2.6 nM and 45 nM. Specifi
c H-3-QNB binding membranes from neural retina exhibited a characteris
tic developmental profile. RPE showed a high density of H-3-QNB bindin
g sites through all developmental periods studied. The major onset of
binding sites is at the time of RPE differentiation. Our data open the
possibility of muscarinic receptors being involved in differentiation
and/or proliferation of RPE.