EVIDENCE FOR FUROSEMIDE-SENSITIVE, CA2+(MG2+)-DEPENDENT, CL- TRANSPORT IN RED-BLOOD-CELLS OF LAMPREY (LAMPETRA-FLUVIATILIS)

1. The kinetics of Cl- uptake and unidirectional Cl- influx were studied in lamprey red blood cells using Cl-36 as a tracer. 2. When the red cells were incubated with Cl-36 in Standard saline containing 1 mM Ca2+ and Mg2+ the steady state distribution for Cl-36 (cell/medium) was 0.16 +/- 0.02 and was achieved within 150 min incubation. Under these conditions the initial rate of Cl- influx was 29 +/- 4 mmol/l cells/hr. 3. The initial rate of Cl- influx was only 9.0 +/- 0.9 mmol/l cells/hr for the red cells incubated in a nominally Ca2+-Mg2+-free medium. Addition of 1 or 5 mM Ca2+ and Mg2+ alone to standard saline produced a concentration dependent stimulation of Cl- influx. Ca2+ ions were about twice as effective in the activation of Cl- influx. 4. Furosemide (1-2 mM) inhibited the rate of Cl- influx to the minimum value of about 5 mmol/l/hr independent of the presence of Ca2+ or Mg2+ ions in the media. 5. The initial furosemide-sensitive Cl- influx was unaffected by an increase of external K+ concentration to 50 mM in the presence of 1 mM Ca2+ and Mg2+ in the medium. The Cl- influx appears not to be associated with the movement of Na+ ions via the erythrocyte membrane. The true mechanism of the furosemide-sensitive Cl- entry in lamprey red cells remains unclear. 6. A residual furosemide-insensitive Cl- influx in the red cells was stimulated by 41% in the presence of 1 mM Ba2+ or 50 mM K+ in media.