Key Points
- To determine the impact of CO2-induced intracellular acidosis and sarcolemmal Na+-H+ exchange on intracellular sodium activity, intracellular pH, and membrane currents in cardiac Purkinje fibres.
- Measured intracellular pH (pHi) and intracellular sodium activity (aiNa) in rabbit cardiac Purkinje fibres using liquid-sensor ion-selective microelectrodes coupled with a two-microelectrode voltage clamp.
- Manipulated pHi by alternating between nominally CO2-free HEPES and CO2-HCO3- buffers, testing responses alongside Na+-K+ pump inhibition, amiloride, barium, and tetrodotoxin.
- Intracellular acidification below pH 7.0 increased aiNa; during K+-free Na+-K+ pump inhibition, the rate of aiNa rise increased to 1.5 +/- 0.2 at 5% CO2 (pHi 7.00), 2.4 +/- 0.1 at 7% CO2 (pHi 6.89), and 3.1 +/- 0.2 at 15% CO2 (pHi 6.74) relative to HEPES (pHi 7.24), an effect blocked by 2 mM amiloride.
- Acidosis induced an early inward holding current shift that reversed at -81.5 mV and was inhibited by 1 mM Ba2+, demonstrating a decrease in K+ conductance, followed by a secondary outward current driven by the Na+-K+ pump.
- Extracellular acidosis (pHo 6.7) reduced the acid-dependent aiNa rise to approximately 10% of control, while active Na+ extrusion and Na+-K+ pump current were suppressed by roughly 30% at pHi 6.7 compared to pHi 7.2.
Structured PICO
PPopulationrabbit cardiac Purkinje fibres
IInterventionCO2 acidosis (alternating nominally CO2-free HEPES buffer and a CO2-HCO3- buffer)
CComparatornominally CO2-free HEPES buffer
OOutcomeintracellular Na+ activity (aiNa), intracellular pH (pHi) and membrane holding current (Ih)surrogate
In rabbit cardiac Purkinje fibres, CO2-induced intracellular acidosis increases intracellular Na+ activity via Na+-H+ exchange, leading to secondary electrophysiological changes including hyperpolarization.