Pacemaker currents in neurons and excitable cells Emilio Carbone
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Transcript of Pacemaker currents in neurons and excitable cells Emilio Carbone
Pacemaker currents in neurons and excitable cells
Emilio Carbone
Summer Course on Experimental NeuroscienceSchool of Neuroscience Department of Neuroscience
Corso Raffaello 30, 10125 TorinoTorino, July 1 2009
Different neuronal APs
from Bean, Nature Review Neurosci. (2007)
Different neuronal APs
Voltage-gated Na+ and K+ channels account for the fast APs
fast activatingfast inactivating
slowly activatingnon inactivating
INa = gNa (Vm – ENa)
IK = gK (Vm – EK)
ENa= +63 mV
EK = -102 mV
Block of V-gated Na+ and K+ channels alter the shape of APs
Ca2+-activated K+ channels do also shape the APs
Ca2+-activated K+ channels do also shape the APs
The big K+ channel (BKCa) Activation is Ca2+- and V-dependent Micromolar affinity for Ca2+
Forms nanodomains with Ca2+ channels Responsible for fast repolarizations Is blocked by charybdotoxin, iberiotoxin, paxilline and 0.5 -1 mM TEA+
Marcantoni et al., Cell Calcium 2007
Ca2+-activated K+ channels do also shape the APs
The small K+ channel (SKCa) Activation is only Ca2+-dependent (regulated by CaM) Submicromolar affinity for Ca2+
Forms microdomains with Ca2+ channels Requires more than one voltage-gated Ca2+ channel to activate Sensitive to the cytoplasmatic Ca2+
Responsible of slow repolarization Is blocked by apamin, insensitive to TEA+ and Cs+
Voltage and Ca2+-gated ion channels contribute to shape the APs
SKCa
circulating adrenaline
vesicle
Ca2+
Ca2+
sympathetic nerve stimulation
action potential
Chromaffin cells undergo spontaneous activity at rest
Preliminary observations to identify a pacemaker channel
Marcantoni et al., Cell Calcium 2007
Marcantoni et al., Cell Calcium 2007
Pacemaker channels require peculiar gating properties
Marcantoni et al., submitted 2009Cesetti et al., J. Neurosci 2003
The L-type channels: Cav1.2, Cav1.3
Ion currents viewed through the “action potential-clamp”
The voltage comand is not a step but the action potential itself previously recorded from the same cell
This technique allows to record the ion currents during the time course of the AP
It is the most direct way to analyze the kinetics of ion channels while the excitable cell is under functional conditions
It can be applied to any type of excitable cell that fires (neuron, cardiac myocytes, neuroendocrine cells, …)
Na+, Ca2+ and K+ currents during the action potential-clamp
INa = gNa (Vm – ENa)
IK = gK (Vm – EK)
ICa = gCa (Vm – ECa)
Inward Na+ and Ca2+ currents in central neurons
from Bean, Nature Review Neurosci. (2007)
Ca2+ currents before and during the AP in chromaffin cells
L-type channels dominate the pre-spike phase with respect to the other high-threshold Ca2+ channels
The experiment suggests that L-type Ca2+ channels are potentially suitable for carrying pacemaker currents during a train of APs
L-type channels carry a pacemaker current in chromaffin cells
In Cav1.3-/- mice a high percentage of chromaffin cells are silent
Strict coupling between L and BKCa channels in central neurons
from Bean, Nature Review Neurosci. (2007)
The agonist BayK 8644 enhances the pacemaker L-type currents
from Albillos et al. EJN. (1996)
from Marcantoni et al. submitted (2009)
from Puopolo et al J Neurosci (2007)
Na+ and Ca2+ pacemaker currents in midbrain dopaminergic neurons
Pacemaker currents in dopaminergic neurons
from Puopolo et al J Neurosci (2007)
L-type channels control the pacemaker current of dopaminergic neurons
Pacemaker currents in suprachiasmatic nucleus (SCN) neurons
from Jackson et al J Neurosci (2004)
Background pacemaker currents in SCN neurons
Suggested readings:
Bean B. (2007) Nature Reviews Neuroscience 8:451
Fakler B & Adelman JP (2008) Neuron 59:873
Marcantoni et al (2009) Pflügers Archiv Europ J Physiol 457:1093
Marcantoni et al (2007) Cell Calcium 42:397
Jackson et al (2004) J. Neuroscience 24:7985
Puopolo et al (2007) J. Neuroscience 27:645