Evidence for an electrogenic Na+-HCO₃− symport in rat cardiac myocytes

• Autores: Aiello, Ernesto Alejandro; Vila Petroff, Martín Gerardo; Mattiazzi, Alicia Ramona; Cingolani, Horacio Eugenio
• Año de publicación: 1998
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Médicas; Hyperpolarization (biology); Biophysics; Internal medicine; Endocrinology; Repolarization; Patch clamp; Membrane potential; Cotransporter; HEPES; Reversal potential; DIDS; Biology
• Institución: Universidad Nacional de La Plata

1. The perforated whole-cell configuration of patch clamp and the pH fluorescent indicator SNARF were used to determine the electrogenicity of the Na+-HCO₃- cotransport in isolated rat ventricular myocytes. 2. Switching from Hepes buffer to HCO₃- buffer at constant extracellular pH (pH_o) hyperpolarized the resting membrane potential (RMP) by 2.9 +/- 0.4 mV (n = 9, P < 0.05). In the presence of HCO₃-, the anion blocker SITS depolarized RMP by 2.6 +/- 0.5 mV (n = 5, P < 0.05). No HCO₃--induced hyperpolarization was observed in the absence of extracellular Na+. The duration of the action potential measured at 50 % of repolarization time (APD₅₀) was 29.2 +/- 6.1 % shorter in the presence of HCO₃- than in its absence (n = 6, P < 0.05). 3. Quasi-steady-state currents were evoked by voltage-clamped ramps ranging from -130 to +30 mV, during 8 s. The development of a novel component of Na+-dependent and Cl--independent steady-state outward current was observed in the presence of HCO₃-. The reversal potential (E_rev) of the Na+-HCO₃- cotransport current (I_Na,Bic) was measured at four different levels of extracellular Na+. A HCO₃-:Na+ ratio compatible with a stoichiometry of 2:1 was detected. I_Na,Bic was also studied in isolation in standard whole-cell experiments. Under these conditions, I_Na,Bic reversed at -96.4 +/- 1.9 mV (n = 5), being consistent with the influx of 2 HCO₃- ions per Na+ ion through the Na+-HCO₃- cotransporter. 4. In the presence of external HCO₃-, after 10 min of depolarizing the membrane potential (Em) with 45 mM extracellular K+, a significant intracellular alkalinization was detected (0.09 +/- 0. 03 pH units; n = 5, P < 0.05). No changes in pHi were observed when the myocytes were pre-treated with the anion blocker DIDS (0.001 +/- 0.024 pH units; n = 5, n.s.), or when exposed to Na+-free solutions (0.003 +/- 0.037 pH units; n = 6, n.s.). 5. The above results allow us to conclude that the cardiac Na+-HCO₃- cotransport is electrogenic and has an influence on RMP and APD of rat ventricular cells.
Facultad de Ciencias Médicas