Evidence for coupled transport of bicarbonate and sodium in cultured bovine corneal endothelial cells

Abstract

Using intracellular microelectrode technique, the response of the voltage V across the plasma membrane of cultured bovine corneal endothelial cells to changes in sodium and bicarbonate concentrations was investigated. (1) The electrical response to changes in [HCO3-]o (depolarization upon lowering and hyperpolarization upon raising [HCO3-]o) was dependent on sodium. Lithium could fairly well be substituted for sodium, whereas potassium or choline were much less effective. (2) Removal of external sodium caused a depolarization, while a readdition led to a hyperpolarization, which increased with time of preincubation in the sodium-depleted medium. (3) The response to changes in [Na+]o was dependent on bicarbonate. In a nominally bicarbonate-free medium, its amplitude was decreased or even reversed in sign. (4) Application of SITS or DIDS (10(-3) M) had a similar effect on the response to sodium as bicarbonate-depleted medium. (5) At [Na+]o = 151 mM and [HCO3-]o = 46 mM, the transients of V depended, with 39.0 +/- 9.0 (SD) mV/decade, on bicarbonate and, with 15.3 +/- 5.8 (SD) mV/decade, on sodium. (6) After the preincubation of cells with lithium, replacement of Li by choline led to similar effects as the replacement of sodium by choline, though the response of V was smaller with Li. This response could be reduced or reversed by the removal of bicarbonate or by the application of SITS. (7) Amiloride (10(-3) M) caused a reversible hyperpolarization of the steady-state potential by 8.5 +/- 2.6 mV (SD). It did not affect the immediate response to changes in [Na+]o or [HCO3-]o, but reduced the speed of regaining the steady-state potential after a change in [HCO3-]o. (8) Ouabain (10(-4) M) caused a fast depolarization of -6.8 +/- 1.1 (SD) mV, which was followed by a continuing slower depolarization. The effect was almost identical at 10(-5) M. (9) It is suggested, that corneal endothelial cells possess a cotransport for sodium and bicarbonate, which transports net negative charge with these ions. It is inhibitable by stilbenes, but not directly affected by amiloride or ouabain. Lithium is a good substitute for sodium with respect to bicarbonate transport and is transported itself. In addition, the effect of amiloride provides indirect evidence for the existence of a Na+/H+-antiport. A model for the transepithelial transport of bicarbonate across the corneal endothelium is proposed.

Bicarbonate-dependent and -independent intracellular pH regulatory mechanisms in rat hepatocytes. Evidence for Na+-HCO3- cotransport.

“…Na'-HCO-cotransport is electrogenic in renal proximal tubular and corneal epithelial cells (20)(21)(22)(23)38); in rabbit proximal tubule, the HCO-/Na' stochiometry is 3:1 (38 Fig. 11 complement data shown in Fig.…”

“…Received for publication 19 CL-/HCO-exchange (15)(16)(17)(18)(19), and (c) Na'-HCO-cotransport (20)(21)(22)(23)(24)(25).…”

Sodium‐bicarbonate cotransport current in identified leech glial cells.

“…4T Munsch and J. W. Deitmer In most epithelial and glial cells, this Na'-HC03-cotransport is electrogenic, and hence sensitive to the membrane potential (Boron & Boulpaep, 1983;Jentsch, Keller, Koch & Wiederholt, 1984;La Cour, 1989;Hughes, Adorante, Miller & Lin, 1989;Deitmer & Szatkowski, 1990;Fitz, Lidofsky, Xie & Scharschmidt, 1992). In retinal Miiller glial cells, the current underlying the Na+-HCO3-cotransport was measured using whole-cell patch-clamp recordings (Newman & Astion, 1991;Newman, 1991).…”

Triflocin, a novel inhibitor for the Na‐HCO3 symport in the proximal tubule

“…This transporter may play a major role in the regulation of the aqueous humour in the eye (Jentsch et al, 1984) and in the control of extracellular pH in the nervous system (Deitmer, 1991). Consequently, novel inhibitors could lead to the development in the near future of a pharmacopoeia that could be applied to some physiopathological states.…”