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Calcium electrogenesis in neocortical pyramidal neurons in vivo
Author(s) -
Paré Denis,
Lang Eric J.
Publication year - 1998
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.1460-9568.1998.00323.x
Subject(s) - depolarization , tetrodotoxin , neuroscience , biophysics , chemistry , in vivo , membrane potential , extracellular , neocortex , orthodromic , slice preparation , electrophysiology , biology , biochemistry , microbiology and biotechnology
Much of what is known about Ca 2+ electrogenesis in neocortical cells has been derived from in vitro studies. Since Ca 2+ currents are controlled by various modulators, comparing these findings to in vivo data is essential. Here, we analysed tetrodotoxin (TTX)‐resistant, presumably Ca 2+ ‐mediated potentials in intracellularly recorded neocortical neurons in vivo . TTX was applied locally to block Na + channels. Its effectiveness was demonstrated by the elimination of fast spikes and orthodromic responses. In response to depolarizing current pulses bringing the membrane potential beyond ≈–33 mV, 71% of neurons generated high‐threshold Ca 2+ spikes averaging 17 mV. This is in contrast with in vitro findings, where high‐threshold spikes could only be elicited following the blockade of K + conductances. Consistent with this, neurons dialysed with K + channel blockers in vivo generated high‐threshold spikes that had a lower threshold (≈–40 mV) and, with intracellular Cs + , a larger amplitude, indicating the presence of K + currents opposing the activation of Ca 2+ channels. Only 15% of cortical cells displayed low‐threshold Ca 2+ spikes. To compare high‐threshold Ca 2+ spikes evoked by synaptic stimuli or current injection, another group of cortical neurons was dialysed with QX‐314 and Cs + , in the absence of extracellular TTX. Synaptic stimuli applied on a background of membrane depolarization elicited presumed Ca 2+ spikes whose amplitude varied in a stepwise fashion. Thus, although there are numerous similarities between in vivo and in vitro data, some significant differences were found, which suggest that the high‐voltage activated Ca 2+ currents and/or the K + conductances that oppose them are subjected to different modulatory influences in vivo than in vitro .