Intracellular Cl Content Research Articles

GABA-mediated trophic effect on oligodendrocytes requires Na-K-2Cl cotransport activity.

The Na-K-2Cl cotransporter isoform1 (NKCC1) is present in many animal cells where it plays prominent roles in regulating cell volume and maintaining intracellular Cl(-) concentration ([Cl(-)]i) above electrochemical equilibrium. We show here that NKCC1 is present and active in cultured oligodendrocytes. Expression of NKCC1 in the rat spinal cord increased during development from postnatal day 6 through 21 in parallel with that of myelin basic protein. In cultured oligodendrocytes, 39% of the total K+ (86Rb+) influx represented NKCC1 activity. Activation of GABA(A) receptors with muscimol produced a reduction in intracellular Cl(-) content, cell shrinkage, and a stimulation of NKCC1 activity. Muscimol also triggered an increase in intracellular Ca2+, which depended on NKCC1 activity. Survival of oligodendrocytes following withdrawal of growth factors was enhanced by muscimol and this effect also required NKCC1 activity. Our results suggest that NKCC1 functions in oligodendrocytes to maintain [Cl(-)]i above electrochemical equilibrium and that NKCC1 is required for GABAergic trophic effects.

Relationship between cell volume and ion transport in the early distal tubule of the Amphiuma kidney.

The roles of apical and basolateral transport mechanisms in the regulation of cell volume and the hydraulic water permeabilities (Lp) of the individual cell membranes of the Amphiuma early distal tubule (diluting segment) were evaluated using video and optical techniques as well as conventional and Cl-sensitive microelectrodes. The Lp of the apical cell membrane calculated per square centimeter of tubule is less than 3% that of the basolateral cell membrane. Calculated per square centimeter of membrane, the Lp of the apical cell membrane is less than 40% that of the basolateral cell membrane. Thus, two factors are responsible for the asymmetry in the Lp of the early distal tubule: an intrinsic difference in the Lp per square centimeter of membrane area, and a difference in the surface areas of the apical and basolateral cell membranes. Early distal tubule cells do not regulate volume after a reduction in bath osmolality. This cell swelling occurs without a change in the intracellular Cl content or the basolateral cell membrane potential. In contrast, reducing the osmolality of the basolateral solution in the presence of luminal furosemide diminishes the magnitude of the increase in cell volume to a value below that predicted from the change in osmolality. This osmotic swelling is associated with a reduction in the intracellular Cl content. Hence, early distal tubule cells can lose solute in response to osmotic swelling, but only after the apical Na/K/Cl transporter is blocked. Inhibition of basolateral Na/K ATPase with ouabain results in severe cell swelling. This swelling in response to ouabain can be inhibited by the prior application of furosemide, which suggests that the swelling is due to the continued entry of solutes, primarily through the apical cotransport pathway.

Efflux du 36Cl et distribution du Cl dans le muscle papillaire du lapin, effet de l'ouabaïne

The 36Cl efflux "in vivo" was measured in the rabbit papillary muscle to determine the Cl distribution in the muscle and to evaluate the effect of ouabain on this parameter. The results obtained for the 36Cl efflux are analyzed using either a two-compartment model or a model including diffusion in the extracellular space in series with one compartment. The Cl exchange with 36Cl, [Cl]i (intracellular Cl content which has participated in exchange, Cl in equilibrium with 36Cl) is computed from the exponential terms of the models. A time exposure of 40 and 80 min to the 36Cl-containing solution led to the same exchange Cl content: 20.5 and 23.9 mmol/kg cells. Addition of ouabain (10(-6) M) slightly increased the rate constant of the cellular compartment, but did not influence the [Cl]i. In the presence of ouabain (10(-6) M), there was a significant increase in the efflux component with a rapid rate constant. These results can be interpreted as follows: the Cl intracellular concentration is not affected by ouabain; thus, the increase in total Cl content induced in the papillary muscle by ouabain is located in a compartment having a very rapid exchange velocity with the extracellular medium.