Topiramate Decelerates Bicarbonate-Driven Acid-Elimination of Human Neocortical Neurons: Strategic Significance for its Antiepileptic, Antimigraine and Neuroprotective Properties

Background: Mammalian central neurons regulate their intracellular pH (pHi) strongly and even slight pHi-fluctuations can influence inter-/intracellular signaling, synaptic plasticity and excitability. Objective: For the first time, we investigated topiramate´s (TPM) influence on pHi- behavior of human central neurons representing a promising target for anticonvulsants and antimigraine drugs. Methods: In slice-preparations of tissue resected from the middle temporal gyrus of five adults with intractable temporal lobe epilepsy, BCECF-AM-loaded neocortical pyramidal-cells were investigated fluometrically. The pHi-regulation was estimated by using the recovery-slope from intracellular acidification after an ammonium-prepulse (APP). Results: Among 17 pyramidal neurons exposed to 50 µM TPM, seven (41.24%) responded with an altered resting-pHi (7.02±0.12), i.e. acidification of 0.01-0.03 pH- units. The more alkaline the neurons, the greater the TPM-related acidifications (r=0.7, p=0.001, n=17). The recovery from APP-acidification was significantly slowed under TPM (p<0.001, n=5). Further experiments using nominal bicarbonate-free (n=2) and chloride-free (n=2) conditions pointed to a modulation of HCO3(-)-driven pHi-regulation by TPM, favoring the stimulation of the passive Cl(-)/HCO3(-)- antiporter (CBT) - an acid-loader predominantly in more alkaline neurons. Conclusion: TPM modulated the bicarbonate-driven pHi-regulation just as previously described in adult guinea-pig hippocampal neurons. We discussed the significance of the resulting subtle acidifications for beneficial antiepileptic, antimigraine and neuroprotective effects as well as for unwanted cognitive deficits. Study Limitations: Although these results are the only available pHi-measurements of human brain neurons to this issue, to the best of our knowledge, the study is limited by the small number of cells analyzed due to limited human material. Thus, the results presented here are preliminary data. Greater sample size is required to reach more reliable conclusions.”

Intracellular pH regulation in human Sertoli cells: role of membrane transporters

Sertoli cells are responsible for regulating a wide range of processes that lead to the differentiation of male germ cells into spermatozoa. Intracellular pH (pHi) is an important parameter in cell physiology regulating namely cell metabolism and differentiation. However, pHi regulation mechanisms in Sertoli cells have not yet been systematically elucidated. In this work, pHi was determined in primary cultures of human Sertoli cells. Sertoli cells were exposed to weak acids, which caused a rapid acidification of the intracellular milieu. pHi then recovered by a mechanism that was shown to be particularly sensitive to the presence of the inhibitor DIDS (4,4′-diisothiocyanostilbene disulfonic acid). In the presence of amiloride and PSA (picrylsulfonic acid), pHi recovery was also significantly affected. These results indicate that, in the experimental conditions used, pHi is regulated by the action of an Na+-driven HCO3−/Cl−exchanger and an Na+/HCO3−co-transporter and also by the action of the Na+/H+exchanger. On the other hand, pHi recovery was only slightly affected by concanamycin A, suggesting that V-Type ATPases do not have a relevant action on pHi regulation in human Sertoli cells, and was independent of the presence of bumetanide, suggesting that the inhibition of the Na+/K+/Cl−co-transporter does not affect pHi recovery, not even indirectly via the shift of ionic gradients. Finally, pHi was shown to be sensitive to the removal of external Cl−, but not of Na+or K+, evidencing the presence of a membrane Cl−-dependent base extruder, namely the Na+-independent HCO3−/Cl−exchanger, and its role on pHi maintenance on these cells.