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

Abstract

The permeability of follicle-enclosed isolated lamprey Lampetra fluviatilis oocytes to chloride was characterized during the pre-spawning season using 36Cl 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 5oC) in December to 7.5 ⋅ 10− 6 cm/s (at 10oC) 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 5-20oC. 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 Cu2+ and 0.2 mM Cd2+ caused acceleration of Cl- influx, while 0.2 mM Pb2+, 0.2 mM Zn2+ and 0.15-5.0 mM (Ca2+ + Mg2+) were without effect. Treatment of the cells with ionophore A23187 in the presence of 5 mM Ca2+ also proved to be ineffective. Bumetanide-sensitive NKCC provided less than 5% of the total Cl- influx. In April, Cu2+ 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.