TY - JOUR

T1 - Calcium conductance and firing properties of spinal motoneurones in the turtle.

AU - Hounsgaard, J.

AU - Mintz, I.

PY - 1988/4/1

Y1 - 1988/4/1

N2 - 1. The contribution of Ca2+ conductance to the firing properties of motoneurones was investigated in transverse slices of the turtle spinal cord. 2. In the presence of tetrodotoxin (TTX), tetraethylamonium (TEA) in low extracellular concentration (less than 5 mM) promoted Ca2+ spikes. In higher concentrations of TEA, a suprathreshold depolarizing current pulse was followed by an after‐discharge of Ca2+ spikes riding on a Ca2+ plateau potential. 3. The Ca2+‐dependent plateau was also promoted by Cs+, 4‐aminopyridine (4‐AP) and apamin. However, Ca2+ spikes during plateaux were an order of magnitude faster when promoted by Cs+ or 4‐AP rather than TEA, and apamin did not promote Ca2+ spikes at all. 4. Ca2+ plateaux but not Ca2+ spikes were blocked by nifedipine. 5. In normal medium all effects of the transient Ca2+ influx during action potentials were attributable to its influence on the slow after‐hyperpolarization. The nifedipine‐sensitive, sustained Ca2+ influx was expressed exclusively as plateau potentials and only under conditions of reduced K+ current. 6. It is concluded that the transient and the sustained Ca2+ fluxes in spinal motoneurones are curtailed by different K+ conductances. The two Ca2+ responses are suggested as being mediated by two different types of Ca2+ channels.

AB - 1. The contribution of Ca2+ conductance to the firing properties of motoneurones was investigated in transverse slices of the turtle spinal cord. 2. In the presence of tetrodotoxin (TTX), tetraethylamonium (TEA) in low extracellular concentration (less than 5 mM) promoted Ca2+ spikes. In higher concentrations of TEA, a suprathreshold depolarizing current pulse was followed by an after‐discharge of Ca2+ spikes riding on a Ca2+ plateau potential. 3. The Ca2+‐dependent plateau was also promoted by Cs+, 4‐aminopyridine (4‐AP) and apamin. However, Ca2+ spikes during plateaux were an order of magnitude faster when promoted by Cs+ or 4‐AP rather than TEA, and apamin did not promote Ca2+ spikes at all. 4. Ca2+ plateaux but not Ca2+ spikes were blocked by nifedipine. 5. In normal medium all effects of the transient Ca2+ influx during action potentials were attributable to its influence on the slow after‐hyperpolarization. The nifedipine‐sensitive, sustained Ca2+ influx was expressed exclusively as plateau potentials and only under conditions of reduced K+ current. 6. It is concluded that the transient and the sustained Ca2+ fluxes in spinal motoneurones are curtailed by different K+ conductances. The two Ca2+ responses are suggested as being mediated by two different types of Ca2+ channels.

UR - http://www.scopus.com/inward/record.url?scp=0023856933&partnerID=8YFLogxK

U2 - 10.1113/jphysiol.1988.sp017059

DO - 10.1113/jphysiol.1988.sp017059

M3 - Journal article

C2 - 2455804

AN - SCOPUS:0023856933

VL - 398

SP - 591

EP - 603

JO - The Journal of Physiology

JF - The Journal of Physiology

SN - 0022-3751

IS - 1

ER -