Summary of Research Project Results under JSPS FY2001
"Research for the Future Program"

1.Research Institution Osaka University
2.Research Area Life Sciences
3.Research Field Cellular Signaling
4.Term of Project FY 1997 〜 FY 2001
5.Project Number 97L00301
6.Title of Project Adaptation Mechanism in Vision and Other Receptors

7.Project Leader
Name Institution,Department Title of Position
Satoru, Kawamura Osaka University, Graduate School of Science Professor

8.Core Members

Names Institution,Department Title of Position
Akimichi, Kaneko Keio University, School of Medicine Professor

9.Summary of Research Results

1. S-modulin is believed to be a Ca-dependent regulator in photoreceptor adaptation. We identified seven amino acid residues as the functional sites of S-modulin.
2. S-modulin is thought to function by increasing the lifetime of light-activated visual pigment. This idea was tested and was found to be the case.
3. There are two types of photoreceptors in vertebrates, rods and cones. The light-sensitivity of a rod is high so that rods are responsible for twilight vision. The light-sensitivity of a cone is low and cones are responsible for daylight vision. We obtained purified rods and cones from carp, and asked why the light-sensitivity of a cone is low. Several reactions in the phototransduction cascade were found to be less effective in cones.
4. Bipolar cells (BCs) have antagonistic center-surround receptive field. We studied the effect of GABA on BCs using gramicidin-perforated patch clamp technique in the mouse retina, and found that GABA depolarizes ON-type BC and hyperpolarizes OFF-type BCs. Our results are consistent with the type of Cl- transporter in BCs and interpret the feed-forward connection from horizontal cell to BC.
5. We examined the spread of electrical signals in dendrites of amacrine cells and found that depolarization was boosted by persistent Na current and Ca current. The action potential conducted from the soma into the dendrite but was modulated by local GABA application. It is suggested that the non-uniform conduction of the action potentials contributes to the formation of directional selectivity.
6. Olfactory adaptation is mediated by an increase in the Ca concentration of olfactory cells. This Ca increase should be detected by Ca-binding proteins. We found a novel Ca-binding protein, p26olf, in the olfactory epithelium. This protein binds to a β-adrenergic receptor kinase-like protein in a Ca-dependent manner, suggesting that p26olf is involved in the olfactory adaptation.

10.Key Words

(1)S-modulin、(2)calcium、(3)cone photoreceptors
(7)bipolar cell、(8)amacrine cell、(9)GABA