We studied the dependence of the expression of protein kinase C immunoreact
ivity (PKC-IR) in the rat retina on the light:dark (LD) cycle and on circad
ian rhythmicity in complete darkness (DD). Two anti-PKC alpha antibodies we
re employed: One, which we call PKC alpha beta recognized the hinge region;
the other, here termed PKC alpha, recognized the regulatory region of the
molecule. Western blots showed that both anti-PKC antibodies stained an ide
ntical single band at approximately 80 kD. The retinal neurons showing PKC-
IR were rod bipolar cells and a variety of amacrine neurons. After 3 weeks
on an LD cycle, PKC alpha beta -IR in both rod bipolar and certain amacrine
cells manifested a clear rhythm with a peak at zeitgeber time (ZT) of 06-1
0 hours and a minimum at ZT 18. No rhythm in total PKC-IR was observed when
using the PKC alpha antibody, but, at ZT 06-10 hours, rod bipolar axon ter
minals showed increased immunostaining. After 48 hours in DD, with either a
ntibody, rod bipolar cells showed increased PKC-IR. The PKC alpha antibody
alone revealed that, after 48 hours, AII amacrine neurons, which lacked PKC
-IR in an LD cycle, manifested marked PKC-IR, which became stronger after 7
2 hours. Light administered early in the dark period greatly increased PKC
alpha beta -IR in rod bipolar and some amacrine neurons. Our data indicate
that light and darkness exert a strong regulatory influence on PKC synthesi
s, activation, and transport in retinal neurons. (C) 2001 Wiley-Liss, Inc.