PT  - JOURNAL ARTICLE
AU  - Ekaterina S. Lobanova
AU  - Stella Finkelstein
AU  - Hongman Song
AU  - Stephen H. Tsang
AU  - Ching-Kang Chen
AU  - Maxim Sokolov
AU  - Nikolai P. Skiba
AU  - Vadim Y. Arshavsky
TI  - Transducin Translocation in Rods Is Triggered by Saturation of the GTPase-Activating Complex
AID  - 10.1523/JNEUROSCI.5010-06.2007
DP  - 2007 Jan 31
TA  - The Journal of Neuroscience
PG  - 1151--1160
VI  - 27
IP  - 5
4099  - http://www.jneurosci.org/content/27/5/1151.short
4100  - http://www.jneurosci.org/content/27/5/1151.full
SO  - J. Neurosci.2007 Jan 31; 27
AB  - Light causes massive translocation of G-protein transducin from the light-sensitive outer segment compartment of the rod photoreceptor cell. Remarkably, significant translocation is observed only when the light intensity exceeds a critical threshold level. We addressed the nature of this threshold using a series of mutant mice and found that the threshold can be shifted to either a lower or higher light intensity, dependent on whether the ability of the GTPase-activating complex to inactivate GTP-bound transducin is decreased or increased. We also demonstrated that the threshold is not dependent on cellular signaling downstream from transducin. Finally, we showed that the extent of transducin α subunit translocation is affected by the hydrophobicity of its acyl modification. This implies that interactions with membranes impose a limitation on transducin translocation. Our data suggest that transducin translocation is triggered when the cell exhausts its capacity to activate transducin GTPase, and a portion of transducin remains active for a sufficient time to dissociate from membranes and to escape from the outer segment. Overall, the threshold marks the switch of the rod from the highly light-sensitive mode of operation required under limited lighting conditions to the less-sensitive energy-saving mode beneficial in bright light, when vision is dominated by cones.