Effect of lithium on rod photoreceptor rhodopsin-coupled G-protein (transducin)

1. Lithium was known to inhibit both adrenergic and cholinergic agonist-induced activation of G-proteins in cerebral cortex. 2. Doly et al (1989) observed that lithium reduced the b-wave of the electroretinogram and suggested that the effect was due to inhibition of G-protein in photoreceptor cells. 3. This study was undertaken to test this hypothesis directly on photoreceptor cell membranes. Rod disk membranes containing the visual transduction machinery were isolated in the dark and the effect of lithium was tested on (a) activation by bright light of G-protein-mediated cyclic GMP hydrolysis, (b) light sensitivity of the activation, (c) the lifetime of the light-activated receptor, and (d) light activation of GTP-gamma-S binding to the membranes. 4. None of these processes were affected by lithium. It is therefore concluded that the effects of lithium on the b-wave of the electroretinogram should be due to influences on G-proteins in other parts of the retina.