Aging is associated with a mild acidification in neocortical human neurons in vitro

The intracellular pH (pHi) in the cytosol of mammalian central neurons is tightly regulated and small pHi-fluctuations are deemed to modulate inter-/intracellular signaling, excitability, and synaptic plasticity. The resting pHi of young rodent hippocampal pyramidal neurons is known to decrease alongside aging for about 0.1 pH-units. There is no information about the relationship between age and pHi of human central neurons. We addressed this knowledge gap using 26 neocortical slices from 12 patients (1-56-years-old) who had undergone epilepsy surgery. For fluorometric recordings, the slice-neurons were loaded with the pHi-sensitive dye BCECF-AM. We found that the pyramidal cells' resting pHi (n=26) descended linearly alongside aging (r=-0.71, p<0.001). This negative relationship persisted, when the sample was confined to specific brain regions (i.e., middle temporal gyrus, 23 neurons, r=-0.68, p<0.001) or pathologies (i.e., hippocampus sclerosis, 8 neurons, r=-0.78, p=0.02). Specifically, neurons (n=9, pHi 7.25 +/- 0.12) from young children (1.5 +/- 0.46-years-old) were significantly more alkaline than neurons from adults (n=17, 38.53 +/- 12.38years old, pHi 7.08 +/- 0.07, p<0.001). Although the samples were from patients with different pathologies the results were in line with those from the rodent hippocampal pyramidal neurons. Like a hormetin, the age-related mild pHi-decrease might contribute to neuroprotection, e.g., via limiting excitotoxicity. On the other hand, aging cortical neurons could become more vulnerable to metabolic overstress by a successive pHi-decrease. Certainly, its impact for the dynamics in short and long-term synaptic plasticity and, ultimately, learning and memory provides a challenge for further research.