E s in a d

pathways, especially those involved in Cl- efflux, in the red Cl- concentration (57.6±5.2 mmol l- 1 cell water), measured using an ion-selective Cl- electrode, showing that ausev and Sherstobitov, 1993). Early findings suggested that e low Cl- flux rates observed for lamprey red blood cells ere due to the absence of the band 3 protein in the erythrocyte embranes of lampreys and hagfish (Ohnishi and Asai, 1985; llory et al. 1987; Tufts and Boutilier,1989). However, recent tudies by Kay et al. (1995) and Cameron et al. (1996) have dicated the presence of genes coding for a protein similar to n anion-transport protein as well as a protein similar to a imeric form of the human anion exchanger AE1 in the rythrocyte membrane of the sea lamprey Petromyzon arinus. The function of these proteins remains unknown. Little is known about the mechanisms of Cl- transport in does not respond to membrane depolarization. Extracellular Ca2+ and Mg2+ play an important role in modulation of its activity (Gusev and Sherstobitov, 1993). Activation of a furosemide-sensitive component of Cl- efflux (different from that mediated by the K+/Cl- cotransporter) has been demonstrated in response to cell swelling (Virkki and Nikinmaa, 1995). The aim of the present investigation was to characterize further Cl- transport pathways across the red blood cell membrane of lamprey, concentrating mainly on Cl- efflux under physiological conditions. The data obtained for Cl- (36Cl) fluxes and cell/medium distribution of 36Cl provide evidenceOne of the remarkable features of the red blood cell membrane of agnathans is an almost complete absence of the rapid DIDS-sensitive Cl- /HCO3- exchange mediated by capnophorin (band 3 protein) that is found in the great majorit