Camilión de Hurtado M C, Pérez N G, Cingolani H E
Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, Argentina.
J Mol Cell Cardiol. 1995 Jan;27(1):231-42.
Experiments were performed in cat papillary muscles in order to explore the possible existence of an electrogenic Na+/HCO3- cotransport. Developed tension (DT), intracellular pH (pHi) with the pH-sensitive dye 2'-7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein (BCECF) and resting membrane potential (Vm) with 3M KCl filled glass microelectrodes were measured. A change from HEPES to HCO3(-)-buffered superfusate induced an immediate decrease in pHi and DT followed by a recovery in which pHi and DT stabilized at values slightly higher than in HEPES buffer. Introduction of HCO3- hyperpolarized Vm by 8 +/- 2.3 mV (P < 0.05). SITS (0.1 mM) completely abolished the hyperpolarization and attenuated the recovery of both pHi and DT. Under steady-state conditions in HCO3- buffered media, SITS induced a depolarization compatible with the suppression of the entry of negative charges. Depolarization by high Ko+ (45 mM) elicited a rise in pHi of 0.07 +/- 0.02 (P < 0.05), that was reversed by returning Ko+ to normal. The depolarization-induced rise in pHi proved to be Na(+)-dependent, SITS sensitive and still occurred after EIPA (microM) blockade. All the evidence strongly supports the existence of an electrogenic Na+/HCO3- cotransport mechanism that participates in the regulation of myocardial pHi. At pHi of 6.94 this mechanism seems to contribute almost equally to the Na+/H+ exchanger to pHi regulation. However, acid equivalent extrusion is potentiated when both the Na+/H+ exchanger and the HCO3-dependent mechanism are simultaneously regulating pHi.
为了探究电生性Na⁺/HCO₃⁻协同转运体可能的存在情况，在猫乳头肌上进行了实验。测量了用pH敏感染料2'-7'-双(2-羧乙基)-5,6-羧基荧光素（BCECF）测定的舒张期张力（DT）、细胞内pH（pHi）以及用3M KCl填充的玻璃微电极测定的静息膜电位（Vm）。从HEPES缓冲液换成HCO₃⁻缓冲的灌流液后，pHi和DT立即下降，随后恢复，其中pHi和DT稳定在略高于HEPES缓冲液中的值。引入HCO₃⁻使Vm超极化8±2.3 mV（P<0.05）。4-乙酰氨基-4'-异硫氰基芪-2,2'-二磺酸（SITS，0.1 mM）完全消除了超极化，并减弱了pHi和DT的恢复。在HCO₃⁻缓冲介质的稳态条件下，SITS引起的去极化与负电荷内流的抑制相一致。高钾（45 mM）引起的去极化使pHi升高0.07±0.02（P<0.05），钾恢复正常后该升高被逆转。去极化诱导的pHi升高被证明是钠依赖性的、SITS敏感的，并且在5-(N-乙基-N-异丙基)amiloride（EIPA，微摩尔）阻断后仍然发生。所有证据都有力地支持了存在一种参与心肌pHi调节的电生性Na⁺/HCO₃⁻协同转运机制。在pHi为6.94时，该机制似乎对pHi调节的贡献与Na⁺/H⁺交换体几乎相同。然而，当Na⁺/H⁺交换体和HCO₃⁻依赖性机制同时调节pHi时，酸当量的排出会增强。
