Shu-Ichi Watanabe

Similar properties of cGMP-activated channels between cones and rods in the carp retina

Using patch-clamp techniques, properties of cGMP-activated channel were studied at a single-channel level in order to examine (1) whether any differences are recognized between the cGMP-activated channels of rods and cones in the same animal species, and (2) whether the channel properties of the same photoreceptor class differ in different animal species. Experiments were performed on inside-out membrane patches excised from outer segments of rods and morphological subtypes of cones in the carp retina. Single-channel activities could be recorded when the patches were perfused with low concentrations of cGMP (less than 10 microM). Throughout five morphological subtypes of cones and rod, single-channel currents showed no significant rectification at membrane hyperpolarization in a low divalent cation solution, and single-channel conductances were almost the same: 13.8 +/- 0.2 pS (mean +/- S.E.M., n = 23) in cones and 12.7 +/- 0.8 pS (n = 3) in rods. These values were significantly smaller than that reported in catfish cones (about 50 pS), and that in rods of the toad and the tiger salamander (about 25 pS). In rods and all subtypes of cones of the carp, open durations of cGMP-activated channels were brief. In addition, kinetic parameters of channel openings and closings showed no differences throughout all subtypes of cones and rod.

Tetrodotoxin-sensitive persistent current boosts the depolarization of retinal amacrine cells in goldfish

To light illumination retinal amacrine cells respond with graded depolarization accompanied by a spike discharge. It has been assumed that the graded depolarization is produced solely by the excitatory synaptic inputs from bipolar cells. Here we demonstrate that a tetrodotoxin (TTX)-sensitive persistent current also contributes to the graded depolarization. This current was isolated in amacrine cells of the goldfish retinal slice preparations by the whole-cell patch clamp technique. The activation threshold of the persistent current was about -50 mV, approximately 10 mV more positive than the membrane potential in the dark. Therefore, it is highly likely that the TTX-sensitive persistent current is a booster of the excitatory postsynaptic potential in amacrine cells.

Preparation and characterization of cationic copolymer latex. 1. Emulsion copolymerization of styrene with 4-vinylpyridine in the presence of non-ionic emulsifier

Abstract A study was made of the effect of 4-vinylpyridine (VP) on the kinetics of the emulsion polymerization of styrene (St) and on the distribution of polymeric VP in the cationic latex. Bimodal distribution of particle diameter was obtained in the polymerization under the conditions of low emulsifier concentration and high VP fraction in monomer feed. This would be caused by insufficient stabilization of resulting particles and by some changes in the character of growing radicals in aqueous phase with conversion. Polymerization under acidic conditions was affected by the amphiphilicity of VP-rich radicals which depended on VP fraction in monomer feed. On the surface of the latex particles prepared at pH 2 polymeric VP located preferentially whereas the latex particles prepared at pH 11 had a nearly statistical distribution of VP on their surface.