Levetiracetam mediates subtle pH-shifts in adult human neocortical pyramidal cells via an inhibition of the bicarbonate-driven neuronal pH-regulation – Implications for excitability and plasticity modulation

• Published in: Brain research Vol. 1710; pp. 146 - 156
• Main Authors: Bonnet, Udo, Bingmann, Dieter, Speckmann, Erwin-Josef, Wiemann, Martin
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.05.2019
• Subjects: Acid/base transporters; Anticonvulsants; Epilepsy; Excitability; Human brain; pH-regulation; Stilbenes; APP; MTG; NCX; AMPA; LIAK; NSAID; Epilepsy; CBE; NHE; SLC; cAMP; NBC; NNN; pHi; MCT2; ASIC; Stilbenes; MAKN; sAC; SV2A; EDIA; Human brain; MACN; DIA; CA; PDS; 0-LE; NBT; V-ATPase; pH-regulation; NCBTs; Excitability; ACSF; BCECF-AM; Acid/base transporters; NBCE; Anticonvulsants; SITS; DIDS; ECS; EIPA; CB2-R; HEPES; ICS; NBCn1; LEV; LIAC; PSD-95
• ISSN: 0006-8993; 1872-6240
• DOI: 10.1016/j.brainres.2018.12.039

•The intracellular pH (pHi)-regulation of human cortical neurons is studied for the first time.•Therapeutic concentrations of the anticonvulsant levetiracetam (LEV) are used.•LEV acidifies neurons with an alkaline pHi which possibly contributes to its anticonvulsive effect.•LEV alkalinizes neurons with an acidic pHi which possibly contributes to its proconvulsive effect.•LEV-induced pHi-shifts are based upon a weakening of HCO3−-driven neuronal pH-regulation. The intracellular pH (pHi) of mammalian central neurons is tightly regulated and small pHi-fluctuations can fine-tune inter-/intracellular signaling, excitability, and synaptic plasticity. The research-gap about the pHi-regulation of human brain neurons is addressed here by testing possible influences of the anticonvulsant levetiracetam (LEV). BCECF-AM-loaded neocortical pyramidal cells were fluorometrically investigated in slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal-lobe epilepsy. Recovery-slope from intracellular acidification following an ammonium prepulse (APP) was used to measure the pHi-regulation. Among twenty pyramidal cells exposed to 50 μM LEV, the resting pHi (7.09 ± 0.14) was lowered in eight (40%) neurons, on average by 0.02 ± 0.011 pH-units. In three (15%) and nine (45%) neurons, a minimal alkaline shift (0.017 ± 0.004 pH-units) and no pHi-shift occurred, respectively. The LEV-induced pHi-shifts were positively correlated with the resting pHi (r = 0.6, p = 0.006, n = 20). In five neurons, which all had responded on LEV with an acidification before, the recovery from APP-acidification was significantly delayed during LEV (p < 0.001). This inhibitory LEV-effect on pHi-regulation i) was similar to that of 200 μM 4,4′-diisothiocyanostilbene-2,2′-disulfonic acid (n = 2) and ii) did not occur under nominal bicarbonate-free conditions (n = 2). Thus, LEV lowered the pHi of human neocortical pyramidal cells most likely by a weakening of the transmembrane HCO3(−)-mediated acid-extrusion. This might contribute to LEV’s anticonvulsive potency. Neurons with more acidic resting pHi-values showed a minimal alkalization upon LEV providing a mechanism for paradoxical proconvulsive LEV-effects rarely observed in epilepsy patients. The significance of these subtle pHi-shifts for cortical excitability and plasticity is discussed.