Properties and function of low- and high-voltage-activated Ca2+ channels in hypoglossal motoneurons.
Calcium influx through voltage-gated Ca2+ channels plays an important role in neuronal function. In a thin-slice preparation of neonatal rat hypoglossal motoneurons (HMs) we recorded Ba2+ currents through voltage-gated Ca2+ channels using the whole-cell configuration of the patch-clamp technique. We found that HMs have low-voltage-activated (LVA) and at least three types of high-voltage-activated (HVA) Ca2+ channels (omega-Aga-IVA sensitive, omega CgTx sensitive, and dihydropyridine sensitive), based on pharmacological and voltage-dependent properties. Of the Ca2+ current activated at 0 mV from a holding potential of -70 mV, approximately one-half was omega-Aga-IVA (200 nM) sensitive, one-third was omega-CgTx (3 microM) sensitive, whereas only 6% was DHP (nimodipine; 10 microM) sensitive. The residual current, after applying these three antagonists, had characteristics of LVA Ca2+ currents. Based on this pharmacology we found that Ca2+ entry during a single action potential (AP) through LVA Ca2+ channels has a different role from CA2+ entry through HVA Ca2+ channels. Ca2+ influx through omega-Aga-IVA-sensitive and omega-CgTx-sensitive HVA Ca2+ channels activates Ca(2+)-activated K+ channels responsible for the AP afterhyperpolarization. On the other hand, Ca2+ entry through LVA Ca2+ channels is responsible for spike afterdepolarization and provides Ca2+ for the Ca(2+)-activated K+ channels that contribute to AP repolarization.
Umemiya
M
M
Department of Physiology and Biophysics, School of Medicine, University of Washington, Seattle 98195.
Berger
A J
AJ
D000818:Animals; D000831:Animals, Newborn; D015220:Calcium Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D004594:Electrophysiology; D005260:Female; D007002:Hypoglossal Nerve / Q000166:cytology / Q000502:physiology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009553:Nimodipine / Q000494:pharmacology; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013111:Spider Venoms / Q000494:pharmacology; D020867:omega-Agatoxin IVA; D020866:omega-Conotoxin GVIA
D015220:Calcium Channels; D010455:Peptides; D013111:Spider Venoms; D020867:omega-Agatoxin IVA; D009553:Nimodipine; D020866:omega-Conotoxin GVIA