IMMUNOLOCALIZATION OF NA,K-ATPASE IN BLOWFLY PHOTORECEPTOR CELLS

The Na,K-ATPase (sodium pump) plays a central role in the physiology o f arthropod photoreceptors as it re-establishes gradients for Na+ and K+ after light stimulation. We have mapped the distribution of the Na, K-ATPase in the photoreceptors of the blowfly (Calliphora liphora eryt hrocephala) by immunofluorescent and immunogold cytochemistry, and dem onstrate that the distribution pattern is more complex than previously presumed. High levels of sodium pumps have been detected consistently in all photoreceptors R1-8 on the nonreceptive surface, but no sodium pumps are found on the microvillar rhabdomere. Within the nonreceptiv e surface of the cells R1-6, however, the sodium pumps are confined to sites juxtaposed to neighboring photoreceptor or glial cells; no sodi um pumps have been detected on the parts of the nonreceptive surface e xposed to the intra-omma-tidial space. In R7 and R8, the sodium pumps are found over the entire nonreceptive surface. The cytoskeletal prote in spectrin colocalizes with the sodium pumps suggesting that linkage of the pump molecules to the spectrin-based submembrane cytoskeleton c ontributes to the maintenance of the complex pattern of pump distribut ion.