Study of Na+/H+ exchange-mediated pHi regulations in neuronal soma and neurites in compartmentalized microfluidic devices

Abstract

Regulation of intracellular pH (pH_i) in neurons is crucial to maintain their physiological function. In the current study, newly-developed polydimethylsiloxane (PDMS) microfluidic devices were used to independently investigate pH_i regulation in neuronal soma and neurites. Embryonic cortical neurons were cultured in PDMS microfluidic devices with soma growing in one chamber (seeded) and neurites extending through a set of perpendicular microchannels into the opposite parallel chamber (non-seeded). Neurons in the microchambers were characterized by the vital dye calcein-red, polarized mitochondria, and expression of neuronal specific β-tubulin (type-III), axonal Tau-1 protein, dendritic microtubule associated protein (MAP-2), and Na⁺/H⁺ exchanger isoform 1 (NHE-1). Neurites exhibited higher resting pH_i than soma (7.16 ± 0.09 vs. 6.90 ± 0.15). The neurites had a proton extrusion rate 3.7-fold faster than in soma following NH₄Cl prepulse-mediated acidification (p < 0.05). The difference in the pH_i regulation rates between neurites and soma can be accounted for by the larger surface area to volume ratio in the neurites. Interestingly, pharmacological inhibition of NHE-1 activity blocked the pH_i regulation in soma and in neurites by ∼70% (p < 0.05). Taken together, our study demonstrated that the microfluidic devices provide a useful tool to study neuronal pH_i regulation in soma and their neurites. We conclude that NHE-1 plays an important role in regulation of pH_i in both compartments.