title: Polarized distribution of Na,K-ATPase in honeybee photoreceptors is maintained by interaction with glial cells.
abstract: Arthropod photoreceptors are polarized cells displaying distinct surface domains. The distribution of the Na,K-ATPase (sodium pump) over these domains was examined in the honeybee photoreceptor using a monoclonal antibody that specifically recognizes the sodium pump alpha-subunit (approximately 100 kDa). We find that the sodium pump is restricted to sites of the nonreceptive photoreceptor surface closely juxtaposed to glial cells; no sodium pumps were detected on the glia-free domains of the nonreceptive surface and on the light-sensitive microvillar membranes. In order to determine the role of photoreceptor-glia contact in maintaining this polarized pump distribution, we assayed the distribution of the Na,K-ATPase after experimentally influencing photoreceptor-glia contact. Sodium pumps were present on the entire nonreceptive photoreceptor surface when photoreceptor-glia contact was removed by isolating the photoreceptors. Remodeling photoreceptor-glia contact by incubation in hyperosmotic saline caused a redistribution of sodium pumps on the photoreceptor surface corresponding to the redistribution of glial cells. We show, further, that both photoreceptor-glia contact and Na,K-ATPase distribution are independent of extracellular Ca2+. No junctional structures were observed at the borders between Na,K-ATPase-positive and Na,K-ATPase-negative membrane domains. Together, these results suggest that adhesion of glial cells to the photoreceptors plays a crucial role in the maintenance of the polarized distribution of Na,K-ATPase in the honeybee photoreceptors. The Ca(2+)-independent adhesion of glial cells to the photoreceptor surface may trap the pump molecules at the sites of photoreceptor-glia contact.
authors.affiliation: Institut für Zoologie, Universität Regensburg, Federal Republic of Germany.
authors.forename: O
authors.initials: O
authors.lastname: Baumann
authors.forename: K
authors.initials: K
authors.lastname: Takeyasu
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D001516:Bees / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002448:Cell Adhesion; D009457:Neuroglia / Q000502:physiology*; D017956:Photoreceptor Cells, Invertebrate / Q000201:enzymology*; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000276:immunology
chemical_list: D000911:Antibodies, Monoclonal; D012462:Saline Solution, Hypertonic; D000254:Sodium-Potassium-Exchanging ATPase; D002118:Calcium