Chloride Transport Across the Plasma Membrane of River Lamprey Oocytes During the Prespawning Period оf Their Life Cycle

The permeability of follicle-enclosed isolated lamprey Lampetra fluviatilis oocytes to chloride was characterized during the pre-spawning season using 36 Cl radioactive tracer. At physiological external [Cl - ] o concentration of 150 mM a steady state equilibrium of the tracer corresponds to an apparent intracellular [Cl - ] i concentration of 10.5 mM in December and 18.6 mM in April, with a half–time for chloride uptake about 20 min. The permeability coefficient for Cl - increased from 1.5 ⋅ 10 − 6 cm/s (at 5 o C) in December to 7.5 ⋅ 10 − 6 cm/s (at 10 o C) in May. The chloride influx was linearly dependent on [Cl - ] o (0–150 mM) and was temperature dependent with an activation energy 24 kJ/mol at 5-20 o C. Depolarization of the plasma membrane in high-K + media in the presence of valinomycin stimulated Cl - influx approximately 2.5-fold. Decreasing medium tonicity resulted in 3-fold activation of Cl - influx compared with isotonic conditions. Exposure of the cells to 0.1–0.2 mM Cu 2+ and 0.2 mM Cd 2+ caused acceleration of Cl - influx, while 0.2 mM Pb 2+ , 0.2 mM Zn 2+ and 0.15-5.0 mM (Ca 2+ + Mg 2+ ) were without effect. Treatment of the cells with ionophore A23187 in the presence of 5 mM Ca 2+ also proved to be ineffective. Bumetanide-sensitive NKCC provided less than 5% of the total Cl - influx. In April, Cu 2+ caused approximately 4,5-fold increase in the amiloride-sensitive component of Na + influx, which most likely represented the NHE mechanism. Obtained results suggest the presence of a channel-mediated entry mechanism for chloride.