title: High potassium promotes differentiation of retinal neurons but does not favor rod differentiation.
abstract: Neural retinal cells of newborn rats were cultured under dissociated culture conditions. Differentiation of several types of retinal cells was confirmed by immunohistochemical detection of type-specific neural phenotypes. We used Thy-1.1 antigen as a ganglion cell marker, HPC-1 or GABA as an amacrine cell marker and rhodopsin as a rod cell marker. With a high concentration of potassium (38 mM), expression of the respective neural phenotypes were differentially affected. High K+ increased the number of Thy-1.1 positive cells 6 to 8 fold, and drastically promoted their neurite extension. The same culture conditions, however, reduced considerably the number of rhodopsin positive cells, possibly due to the unique membrane properties of photoreceptors. A high K+ concentration also promoted differentiation of HPC-1 positive and GABA positive cells, but to a lesser extent than the Thy-1.1 positive cells. Several possibilities were examined to understand the effect of a high K+ concentration on retinal neural cells. The total cell number in cultures with a high K+ concentration was approximately half of that in control cultures at day 3 and slightly smaller at day 11, suggesting that high K+ did not have a positive general effect on the proliferation or survival of retinal cells. Naturally occurring neuronal death (apoptosis) is a well-known phenomenon during retinal development. A histochemical method for detecting DNA fragmentation, a step preceding apoptosis, showed that high K+ had no preventive effect. BrdU (bromodeoxyuridine) immunohistochemistry showed that high K+ did not seem to enhance proliferation of neural precursor cells. These results indicate that a high K+ concentration promotes the expression of neuronal phenotypes but is not a favorable condition for rod differentiation. Since a high K+ concentration is considered to induce depolarization of nerve cells, the present results suggest an anterograde influence from surrounding neuronal cells, through chronic depolarization by elevated K+, is essential for the differentiation and maturation of retinal cells.
authors.affiliation: Laboratory of Neurobiology, Osaka, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Araki
authors.forename: S
authors.initials: S
authors.lastname: Tonè
authors.forename: K
authors.initials: K
authors.lastname: Akagawa
authors.forename: H
authors.initials: H
authors.lastname: Kimura
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D015415:Biomarkers / Q000737:chemistry; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D004249:DNA Damage; D007124:Immunoenzyme Techniques; D008858:Microscopy, Phase-Contrast; D009474:Neurons / Q000737:chemistry / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D012160:Retina / Q000737:chemistry / Q000166:cytology / Q000187:drug effects*; D017948:Retinal Rod Photoreceptor Cells / Q000737:chemistry / Q000166:cytology / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000032:analysis
chemical_list: D015415:Biomarkers; D005680:gamma-Aminobutyric Acid; D011188:Potassium