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A blocker‐resistant, fast‐decaying, intermediate‐threshold calcium current in palaeocortical pyramidal neurons
Author(s) -
Magistretti Jacopo,
Brevi Sara,
De Curtis Marco
Publication year - 2000
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.1460-9568.2000.00125.x
Subject(s) - depolarization , channel blocker , chemistry , biophysics , patch clamp , piriform cortex , extracellular , time constant , calcium , analytical chemistry (journal) , endocrinology , biochemistry , receptor , biology , electrical engineering , organic chemistry , engineering , chromatography , central nervous system
The whole‐cell patch‐clamp technique was used to record Ca 2+ currents in acutely dissociated neurons from layer II of guinea‐pig piriform cortex (PC). Ba 2+ (5 m m ) was used as charge carrier. In a subpopulation of layer II cells (≈ 22%) total Ba 2+ 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 Ca 2+ ‐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 bi‐exponential time course, with a fast time constant of ≈ 20 ms and a slower time constant of ≈ 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 ≈ 7–9 mV in the negative direction in comparison with those of other pharmacologically and/or kinetically different high‐voltage‐activated Ca 2+ currents. We named this blocker‐resistant, fast‐decaying, intermediate‐threshold current I Rfi . The amplitude of I Rfi decreased only slightly (by ≈ 9%) when extracellular Ca 2+ was substituted for Ba 2+ , in contrast with that of slowly decaying, high‐voltage‐activated currents, which was reduced by ≈ 41% on average. Moreover, I Rfi was substantially inhibited by low concentrations of Ni 2+ (50 μ m ). We conclude that I Rfi , because of its fast inactivation kinetics, intermediate threshold of activation and resistance to organic blockers, represents a definite, identifiable Ca 2+ current different from classical high‐voltage‐activated currents and clearly distinguishable from classical I T . The striking similarity found between I Rfi and Ca 2+ currents resulting from heterologous expression of α 1E ‐type channel subunits is discussed.