We are interested in understanding the role of modulation of the cGMP-sensitivity of cyclic-nucleotide gated (CNG) channels by intrinsic factors present in the retina. Our group has identified a novel mechanism for modulating CNG channels involving changes in tyrosine phosphorylation. We have shown that the cGMP-sensitivity of CNG channels increases in intact retina after exposure to IGF- 1, a growth factor intrinsic to the retina, and is due to changes in tyrosine phosphorylation. The ability to study this phenomenon has been facilitated by the ability to express active CNG channels in Xenopus oocytes. Patches excised from oocytes expressing homomeric a-CNG channels become more sensitive to cGMP in the absence of ATP. Pharmacological evidence indicates that this modulation of cGMP-sensitivity is due to changes in tyrosine phosphorylation. CNG channels expressed in oocytes also show a marked increase in the cGMP-sensitivity after IGF- 1 treatment, indicating that the oocyte expression system may be a useful model to study this phenomenon. However, native CNG channels expressed in rod outer segments (ROS) are heterotetramers consisting of two a and two b subunits. There is no research to date concerning the b-subunit in modulation via changes in tyrosine phosphorylation. This proposal will study the mechanism of modulation of the cGMP-sensitivity of CNG channels by the b-subunit. Further studies will be done to measure directly, through biochemical methods, changes in the tyrosine phosphorylation level of the b-subunit due to exposure to growth factors, such as IGF- 1, both in oocytes and intact retina.
|Molokanova, Elena; Krajewski, Jeffrey L; Satpaev, Daulet et al. (2003) Subunit contributions to phosphorylation-dependent modulation of bovine rod cyclic nucleotide-gated channels. J Physiol 552:345-56|
|Krajewski, Jeffrey L; Luetje, Charles W; Kramer, Richard H (2003) Tyrosine phosphorylation of rod cyclic nucleotide-gated channels switches off Ca2+/calmodulin inhibition. J Neurosci 23:10100-6|