A blocker-resistant, fast-decaying, intermediate-threshold calcium current in palaeocortical pyramidal neurons

Jacopo Magistretti, Sara Brevi, Marco De Curtis

Research output: Contribution to journalArticle

Abstract

The whole-cell patch-clamp technique was used to record Ca2+ currents in acutely dissociated neurons from layer II of guinea-pig piriform cortex (PC). Ba2+ (5 mM) was used as charge carrier. In a subpopulation of layer II cells (approximate 22%) total Ba2+ currents (I(Ba)s) displayed a high degree (> 70%) of inactivation after 300 ms of steady depolarization. The application of L-, N- and P/Q-type Ca2+-channel blockers to these high-decay I(Ba)s left their fast inactivating component largely unaffected. The inactivation phase of the blocker-resistant, fast-decaying I(Ba) thus isolated had a hi-exponential time course, with a fast time constant of approximate 20 ms and a slower time constant of approximate 100 ms at voltage levels positive to -10 mV. The voltage dependence of activation of the blocker-resistant, fast-decaying I(Ba) was shifted by approximate 7-9 mV in the negative direction in comparison with those of other pharmacologically and/or kinetically different high-voltage-activated Ca2+ currents. We named this blocker-resistant, fast-decaying, intermediate-threshold current I(Rfi). The amplitude of I(Rfi) decreased only slightly (by approximate 9%) when extracellular Ca2+ was substituted for Ba2+, in contrast with that of slowly decaying, high-voltage-activated currents, which was reduced by approximate 41% on average. Moreover, I(Rfi) was substantially inhibited by low concentrations of Ni2+ (50 μM). We conclude that I(Rfi), because of its fast inactivation kinetics, intermediate threshold of activation and resistance to organic blockers, represents a definite, identifiable Ca2+ current different from classical high-voltage-activated currents and clearly distinguishable from classical I(T). The striking similarity found between I(Rfi) and Ca2+ currents resulting from heterologous expression of α(1E)-type channel subunits is discussed.

Original languageEnglish
Pages (from-to)2376-2386
Number of pages11
JournalEuropean Journal of Neuroscience
Volume12
Issue number7
DOIs
Publication statusPublished - 2000

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Keywords

  • Guinea pig
  • Patch clamp
  • Piriform cortex
  • R-type channels

ASJC Scopus subject areas

  • Neuroscience(all)

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