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Developmental changes in the expression of low‐voltage‐activated Ca 2+ channels in rat visual cortical neurones
Author(s) -
Tarasenko A. N.,
Isaev D. S.,
Eremin A. V.,
Kostyuk P. G.
Publication year - 1998
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.1469-7793.1998.385bn.x
Subject(s) - nifedipine , chemistry , visual cortex , patch clamp , biophysics , cerebral cortex , endocrinology , medicine , calcium , neuroscience , receptor , biology , biochemistry , organic chemistry
1 The functional properties of low‐voltage‐activated (LVA) Ca 2+ channels were studied in pyramidal neurones from different rat visual cortical layers in order to investigate changes in their properties during early postnatal development. Ca 2+ currents were recorded in brain slices using the whole‐cell patch‐clamp technique in rats from three age groups: 2, 3 and 12 days old (postnatal day (P) 2, P3 and P12). 2 It was demonstrated that LVA Ca 2+ currents are present in neurones from superficial (I‐II) and deep (V‐VI) visual cortex layers of P2 and P3 rats. No LVA Ca 2+ currents were observed in neurones from the middle (III‐IV) layers of these rats. The LVA Ca 2+ currents observed in P2 and P3 neurones from both superficial and deep layers could be completely blocked by nifedipine (100 μM) and were insensitive to Ni 2+ (25 μM). 3 The density of LVA Ca 2+ currents decreased rapidly during the early stages of postnatal development, while the density of high‐voltage‐activated (HVA) Ca 2+ currents progressively increased up to the twelfth postnatal day. No LVA Ca 2+ currents were found in P12 neurones from any of the layers. Only HVA Ca 2+ currents with high sensitivity to F − applied through the patch pipette were observed. 4 The kinetics of LVA Ca 2+ currents could be well approximated by the m 2 h Hodgkin‐Huxley equation with an inactivation time constant of 24 ± 6 ms. The steady‐state inactivation curve fitted by a Boltzmann function had the following parameters: membrane potential at half‐inactivation, ‐86.9 mV; steepness coefficient,3.4 mV. 5 It is concluded that, in visual cortical neurones, LVA Ca 2+ channels are expressed only in the neurones of deep and superficial layers over a short period during the earliest postnatal stages. These channels are nifedipine sensitive and similar in functional properties to those in the laterodorsal (LD) thalamic nucleus. However, the cortical neurones do not express another (‘slow’) type of LVA Ca 2+ channel, which is permanently present in LD thalamic neurones after the second postnatal week, indicating that the developmental time course of cortical and thalamic cellsdifferent.