Characterisation of Mechanically Activated Currents in Dorsal Root Ganglia Neurones

1
Neurons were Stimulated Using a Piezo-Electric
Controlled Heat-Polished Glass Pipette

• Perforated Patch
• Configuration
• Neurons 1 day
• in culture
• Tests
• Series 2?m increments
• Repeated stimulus

2
Characterisation of Mechanically Activated
Currents in Dorsal Root Ganglia Neurons

• LJ Drew, TM Jessell, JN Wood
• P Cesare

3
Capsaicin Sensitive and Insensitive Neurons
are Differentially Responsive to
Mechanical Stimulation
Stimuli
12
mm
0
Inward Currents
3000
0
2000
Current Amplitude (pA)
-3000
0
1000
pA
0
-600
0
2
4
6
8
10
12
0
Displacement (mm)
-500
Caps - Slowly adapting
0
300
Caps Rapidly adapting
Time (msec)
4
Blockade of MA Currents by Ruthenium Red and
Gadolinium in Different Subpopulations
100
100
Inhibition
50
50
0
0
0.1
1
10
100
0.1
1
10
100
Log10 Gd3 (mM)
Log10 Ruthenium Red (mM)
Caps Rapidly adapting
Caps - Rapidly adapting
Caps - Slowly adapting
5
MA Currents in Subsets of DRG Neurons are
Differentially Modulated by Ca2
Caps -
0mM Ca2
0
100
pA
-500
50
5mM Ca2
-1000
Control (2mM Ca2)
0
Caps
0
-50
-400
pA
Caps -
5mM Ca2
-100
Caps
Control
-800
0mM Ca2
6
MA Currents Are Acutely Inhibited by Cytochalasin
B (10?M) in Capsaicin Insensitive Neurons
P 0.0001
100
80
60
Control
40
20
0
Caps
Caps -
7
Are MA Currents ASIC Mediated?

• ASIC2 and ASIC3 KO Mice show moderate changes in
  mechanosensitivity.
• Magnitude of MA currents does not correlate with
  rapidly adapting low pH evoked currents.
• MA currents are not modulated by low pH.
• MA currents are not sensitive to Amiloride.
• MA currents are blocked by 300?M Zn2.

8
Conclusions

• Important aspects of the mechanosensitive
  phenotype of DRG neurons are maintained in vitro.
• Pharmacology MA Currents are mediated by closely
  related ion channels in low- and high-threshold
  neurons.
• Ca2 modulation reveals diversity in MA current
  modulation.
• Sensitivity of ion channels may be determined by
  cytoskeletal tethering.