Calcium spikes and calcium plateaux evoked by differential polarization in dendrites of turtle motoneurones in vitro

TY - JOUR

T1 - Calcium spikes and calcium plateaux evoked by differential polarization in dendrites of turtle motoneurones in vitro

AU - Hounsgaard, J

AU - Kiehn, O

PY - 1993

Y1 - 1993

N2 - The ability of dendrites in turtle motoneurones to support calcium spikes and calcium plateaux was investigated using differential polarization by applied electric fields. 2. Electric fields were generated by passing current through transverse slices of the turtle spinal cord between two plate electrodes. The linear extracellular voltage gradient generated by the field implied that the tissue was ohmic and homogeneous. 3. The transmembrane potential at the cell body of motoneurones was measured as the voltage difference between an intracellular and an extracellular microelectrode. 4. In normal medium an applied field induced synaptic activity as well as intrinsic polarization of motoneurones. Synaptic activity was suppressed by tetrodotoxin (TTX, 1 microM). 5. In the presence of TTX and tetraethylammonium (TEA, 1-5 mM), applied fields evoked multicomponent Ca2+ spikes in both the soma-hyperpolarizing and soma-depolarizing direction of the field. The different components of Ca2+ spikes were discrete and additive. High amplitude components had higher threshold and faster time course and were followed by larger after-hyperpolarizations, than low amplitude components. The frequency of field-evoked regenerative responses was relatively insensitive to somatic bias current. 6. TTX-resistant Ca(2+)-mediated plateau potentials promoted by apamin were evoked by differential polarization in both the soma-depolarizing and soma-hyperpolarizing direction. 7. It is concluded that Ca2+ channels responsible for Ca2+ spikes and Ca2+ plateaux are present in dendrites of spinal motoneurones of the turtle.

AB - The ability of dendrites in turtle motoneurones to support calcium spikes and calcium plateaux was investigated using differential polarization by applied electric fields. 2. Electric fields were generated by passing current through transverse slices of the turtle spinal cord between two plate electrodes. The linear extracellular voltage gradient generated by the field implied that the tissue was ohmic and homogeneous. 3. The transmembrane potential at the cell body of motoneurones was measured as the voltage difference between an intracellular and an extracellular microelectrode. 4. In normal medium an applied field induced synaptic activity as well as intrinsic polarization of motoneurones. Synaptic activity was suppressed by tetrodotoxin (TTX, 1 microM). 5. In the presence of TTX and tetraethylammonium (TEA, 1-5 mM), applied fields evoked multicomponent Ca2+ spikes in both the soma-hyperpolarizing and soma-depolarizing direction of the field. The different components of Ca2+ spikes were discrete and additive. High amplitude components had higher threshold and faster time course and were followed by larger after-hyperpolarizations, than low amplitude components. The frequency of field-evoked regenerative responses was relatively insensitive to somatic bias current. 6. TTX-resistant Ca(2+)-mediated plateau potentials promoted by apamin were evoked by differential polarization in both the soma-depolarizing and soma-hyperpolarizing direction. 7. It is concluded that Ca2+ channels responsible for Ca2+ spikes and Ca2+ plateaux are present in dendrites of spinal motoneurones of the turtle.

KW - Animals

KW - Calcium

KW - Calcium Channels

KW - Dendrites

KW - Electric Stimulation

KW - Evoked Potentials

KW - Membrane Potentials

KW - Motor Neurons

KW - Potassium Channels

KW - Synapses

KW - Tetraethylammonium

KW - Tetraethylammonium Compounds

KW - Tetrodotoxin

KW - Turtles

U2 - 10.1113/jphysiol.1993.sp019769

DO - 10.1113/jphysiol.1993.sp019769

M3 - Journal article

C2 - 8254508

SN - 0022-3751

VL - 468

SP - 245

EP - 259

JO - The Journal of Physiology

JF - The Journal of Physiology

IS - 1

ER -