Villa-Abrille María C, Petroff Martín G Vila, Aiello Ernesto A
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, 60 y 120, La Plata 1900, Argentina.
J Physiol. 2007 Feb 1;578(Pt 3):819-29. doi: 10.1113/jphysiol.2006.120170. Epub 2006 Nov 30.
Perforated whole-cell configuration of patch clamp was used to determine the contribution of the electrogenic Na+/HCO3- cotransport (NBC) on the shape of the action potential in cat ventricular myocytes. Switching from Hepes to HCO3- buffer at constant extracellular pH (pH(o)) hyperpolarized resting membrane potential (RMP) by 2.67 +/- 0.42 mV (n = 9, P < 0.05). The duration of action potential measured at 50% of repolarization time (APD50) was 35.8 +/- 6.8% shorter in the presence of HCO3- than in its absence (n = 9, P < 0.05). The anion blocker SITS prevented and reversed the HCO3- -induced hyperpolarization and shortening of APD. In addition, no HCO3- -induced hyperpolarization and APD shortening was observed in the absence of extracellular Na+. Quasi-steady-state currents were evoked by 8 s duration voltage-clamped ramps ranging from -130 to +30 mV. A novel component of SITS-sensitive current was observed in the presence of HCO3-. The HCO3- -sensitive current reversed at -87 +/- 5 mV (n = 7), a value close to the expected reversal potential of an electrogenic Na+/HCO3- cotransport with a HCO3-:Na+ stoichiometry ratio of 2: 1. The above results allow us to conclude that the cardiac electrogenic Na+/HCO3- cotransport has a relevant influence on RMP and APD of cat ventricular cells.
采用膜片钳的穿孔全细胞模式来确定电中性Na⁺/HCO₃⁻协同转运体（NBC）对猫心室肌细胞动作电位形态的影响。在细胞外pH值（pH(o)）恒定的情况下，将细胞外缓冲液从Hepes换成HCO₃⁻，静息膜电位（RMP）超极化2.67±0.42 mV（n = 9，P < 0.05）。在存在HCO₃⁻时，动作电位在复极化时间50%时测量的时程（APD50）比不存在时缩短了35.8±6.8%（n = 9，P < 0.05）。阴离子阻滞剂SITS可预防并逆转HCO₃⁻诱导的超极化以及APD的缩短。此外，在没有细胞外Na⁺的情况下，未观察到HCO₃⁻诱导的超极化和APD缩短。通过持续8 s、电压钳制范围从-130到+30 mV的斜坡电压诱发准稳态电流。在存在HCO₃⁻的情况下观察到一种新的SITS敏感电流成分。HCO₃⁻敏感电流在-87±5 mV处反转（n = 7），该值接近电中性Na⁺/HCO₃⁻协同转运体（HCO₃⁻:Na⁺化学计量比为2:1）预期的反转电位。上述结果使我们得出结论，心脏电中性Na⁺/HCO₃⁻协同转运体对猫心室细胞的RMP和APD有显著影响。
