Document Detail


Stepwise repolarization from Ca2+ plateaus in neocortical pyramidal cells: evidence for nonhomogeneous distribution of HVA Ca2+ channels in dendrites.
MedLine Citation:
PMID:  8229187     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Although cortical dendrites have classically been thought of as passive structures, recent evidence suggests that active conductances, including Ca2+ conductance, are also present in the dendritic membrane. To investigate this, we have recorded intracellularly in slices of rat neocortex bathed in 24 mM tetraethylammonium chloride and 1 microM TTX. Under these conditions, pyramidal neurons generated prolonged Ca2+ spikes. In computer simulations, the breakpoint voltage from which the plateau level began to repolarize was closely related to a specific region on the voltage/activation curve of the high-voltage-activated Ca2+ conductance underlying the spike. This modeling result was supported by the experimental observation that substituting Ba2+ for Ca2+ caused a hyperpolarizing shift in breakpoint voltage by 8-10 mV. Often there was stepwise repolarization from the Ca2+ spike to one or more additional plateau levels. In compartmental computer models, this could be simulated by two different mechanisms: (1) the presence of multiple, electrotonically separated sites of Ca2+ spike electrogenesis in the dendritic tree, and (2) the presence of Ca2+ channels with different voltage dependencies in the same compartment. In experiments, brief hyperpolarizing pulses could cut short the high-amplitude plateau without terminating the smaller "steps." This result could be simulated by both computer models. However, only the multicompartmental model could simulate effects of prolonged depolarizing and hyperpolarizing currents on the breakpoint. Thus, the more depolarized the breakpoint, and hence the closer the spike initiation zone to the recording site, the less it was affected by the injected current. In experiments, the ratio of the breakpoint voltages for the different plateau levels was equal to the ratio of the highest repolarization rates. These data indicate that the breakpoint voltage and the time course of repolarization were the same at all the sites of Ca2+ electrogenesis. Our findings provide strong evidence that Ca2+ spike initiation occurs at electrotonically separated "hot spots" in the dendrites, and that voltage dependence of the Ca2+ channels that underlie the spikes is the same at all sites.
Authors:
I Reuveni; A Friedman; Y Amitai; M J Gutnick
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  The Journal of neuroscience : the official journal of the Society for Neuroscience     Volume:  13     ISSN:  0270-6474     ISO Abbreviation:  J. Neurosci.     Publication Date:  1993 Nov 
Date Detail:
Created Date:  1993-12-08     Completed Date:  1993-12-08     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  8102140     Medline TA:  J Neurosci     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  4609-21     Citation Subset:  IM    
Affiliation:
Department of Physiology, Corob Center for Medical Research, Faculty of Health Sciences, Ben Gurion University of the Negev, Beersheva, Israel.
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MeSH Terms
Descriptor/Qualifier:
Animals
Calcium / metabolism*
Calcium Channels / metabolism*
Cerebral Cortex / drug effects,  physiology*
Dendrites / physiology*
Electric Conductivity / drug effects
Guinea Pigs
Mathematics
Membrane Potentials / drug effects
Models, Neurological
Neurons / drug effects,  physiology*
Pyramidal Tracts / drug effects,  physiology*
Rats
Rats, Sprague-Dawley
Tetraethylammonium
Tetraethylammonium Compounds / pharmacology
Tetrodotoxin / pharmacology
Chemical
Reg. No./Substance:
0/Calcium Channels; 0/Tetraethylammonium Compounds; 4368-28-9/Tetrodotoxin; 66-40-0/Tetraethylammonium; 7440-70-2/Calcium

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine


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