Effects of extracellular pH on the interaction of sipatrigine and lamotrigine with high-voltage-activated (HVA) calcium channels in dissociated neurones of rat cortex

Atticus H. Hainsworth, Francesca Spadoni, Franco Lavaroni, Bernardi Giorgio Bernardi, Alessandro Stefani

Research output: Contribution to journalArticle

Abstract

Acidic extracellular pH reduced high-voltage-activated (HVA) currents in freshly isolated cortical pyramidal neurones of adult rats, shifting activation to more positive voltages (V1/2=-18 mV at pH 7.4, -11 mV at pH 6.4). Sipatrigine inhibited HVA currents, with decreasing potency at acidic pH (IC50 8 μM at pH 7.4, 19 μM at pH 6.4) but the degree of maximal inhibition was >80% in all cases (pH 6.4-8.0). Sipatrigine has two basic groups (pKA values 4.2, 7.7) and at pH 7.4 is 68% in monovalent cationic form and 32% uncharged. From simple binding theory, the pH dependence of sipatrigine inhibition indicates a protonated group with pKA 6.6. Sipatrigine (50 μM) shifted the voltage dependence of channel activation at pH 7.4 (-7.6 mV shift) but not at pH 6.4. Lamotrigine has one basic site (pKA 5.5) and inhibited 34% of the HVA current, with similar potency over the pH range 6.4-7.4 (IC50 7.5-9 μM). These data suggest that the sipatrigine binding site on HVA calcium channels binds both cationic and neutral forms of sipatrigine, interacts with a group with pKA=6.6 and with the channel activation process, and differs from that for lamotrigine. Crown

Original languageEnglish
Pages (from-to)784-791
Number of pages8
JournalNeuropharmacology
Volume40
Issue number6
DOIs
Publication statusPublished - May 2001

Keywords

  • 619C89
  • Activation
  • Calcium channels
  • Lamotrigine
  • Neuroprotection
  • Sipatrigine

ASJC Scopus subject areas

  • Cellular and Molecular Neuroscience
  • Drug Discovery
  • Pharmacology

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