Ni2+ slows the activation kinetics of high-voltage-activated Ca2+ currents in cortical neurons: Evidence for a mechanism of action independent of channel-pore block

J. Magistretti, S. Brevi, M. De Curtis

Research output: Contribution to journalArticle

Abstract

The effects of Ni2+ were evaluated on slowlydecaying, high-voltage-activated (HVA) Ca2+ currents expressed by pyramidal neurons acutely dissociated from guinea-pig piriform cortex. Whole-cell, patch-clamp recordings were performed with Ba2+ as the charge carrier. Ni2+ blocked HVA Ba2+ currents (IBas) with an EC50 of approximately 60 μM. Additionally, after application of nonsaturating Ni2+ concentrations, residual currents activated with substantially slower kinetics than both total and Ni2+-sensitive IBas. None of the pharmacological components of slowly decaying, HVA currents activated with kinetics significantly different from that of total currents, indicating that the effect of Ni2+ on IBas kinetics cannot be attributed to the preferential inhibition of a fast-activating component. The effect of Ni2+ on IBa amplitude was voltage-independent over the potential range normally explored in our experiments (-60 to +20 mV), hence the Ni2+-dependent decrease of IBa activation rate is not due to a voltage- and time-dependent relief from block. Moreover, Ni2+ significantly reduced IBa deactivation speed upon repolarization, which also is not compatible with a depolarization-dependent unblocking mechanism. The dependence on Ni2+ concentration of the IBa activation-rate reduction was remarkably different from that found for IBa block, with an EC50 of ∼20 μM and a Hill coefficient of ∼1.73 vs. ∼1.10. These results demonstrate that Ni2+, besides inhibiting the IBas under study probably by exerting a blocking action on the pore of the underlying Ca2+ channels, also interferes with Ca2+-channel gating kinetics, and strongly suggest that the two effects depend on Ni2+ occupancy of binding sites at least partly distinct.

Original languageEnglish
Pages (from-to)243-262
Number of pages20
JournalJournal of Membrane Biology
Volume179
Issue number3
DOIs
Publication statusPublished - Feb 1 2001

Keywords

  • Activation kinetics
  • Block
  • Calcium currents
  • Channel gating
  • Nickel
  • Patch clamp

ASJC Scopus subject areas

  • Biophysics
  • Physiology
  • Cell Biology

Fingerprint Dive into the research topics of 'Ni2+ slows the activation kinetics of high-voltage-activated Ca2+ currents in cortical neurons: Evidence for a mechanism of action independent of channel-pore block'. Together they form a unique fingerprint.

Cite this