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Biophysical and pharmacological diversity of high‐voltage‐activated calcium currents in layer II neurones of guinea‐pig piriform cortex
Author(s) -
Magistretti Jacopo,
Brevi Sara,
Curtis Marco
Publication year - 1999
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.1999.0705p.x
Subject(s) - nifedipine , piriform cortex , chemistry , calcium channel , barium , voltage dependent calcium channel , calcium , biophysics , patch clamp , endocrinology , biology , biochemistry , receptor , inorganic chemistry , organic chemistry , central nervous system
1 High‐voltage‐activated calcium currents were studied with the whole‐cell, patch‐clamp technique in acutely dissociated pyramidal neurones from guinea‐pig piriform cortex layer II. Barium ions were used as charge carriers. 2 Barium currents ( I Ba ) displayed a remarkable kinetic diversity in different neurones. The ratio between the current amplitude at the end of the test pulses and the peak amplitude ( R e/p ) showed two frequency‐distribution peaks at approximately 0.4 and 0.8. The index of current activation speed (rise time 10‐90 %) directly correlated with the index of current persistence, R e/p . 3 The half‐activation potential ( V ½ ) of total I Ba s positively correlated with the R e/p of the corresponding currents. This implied that the high‐decay I Ba s also had a more negative voltage range of activation than the more persistent ones. 4 The L‐ and N‐type channel blockers nifedipine (10 μ m ) and ω‐conotoxin GVIA (ω‐CTx GVIA, 0.5‐1 μ m ) additively blocked 20 and 25 % of the total I Ba , respectively. The P/Q‐type calcium channel blockers ω‐agatoxin IVA (100 nM), ω‐conotoxin MVIIC (1 μ m ) and 3.3 funnel toxin (1 μ m ), had little effect on I Ba . 5 The nifedipine‐ and ω‐CTx GVIA‐sensitive current had a R e/p > 0.55 and their voltage dependence of activation was of the high‐voltage‐activated type ( V ½ ≈ 0 mV). 6 High‐, intermediate‐ and low‐decay blocker‐resistant currents were observed in different neurones. Their R e/p values highly correlated with those of the corresponding total I Ba s and with the voltage dependence of activation of the underlying conductances. Exponential fittings of the inactivation phase of blocker‐resistant currents returned very fast time constants (lower than 30 ms) for high‐decay currents ( R e/p < 0.25). The intermediate‐decay currents ( R e/p ≈ 0.55) could not derive from variable combinations of high‐ and low‐decay current components. 7 Our data demonstrate a remarkable variety in voltage‐activated calcium currents expressed by piriform cortex neurones, that include currents resistant to high‐voltage‐activated calcium‐channel blockers.