Properties and function of low- and high-voltage-activated Ca2+ channels in hypoglossal motoneurons

Abstract

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.

Reduction of Calcium Currents by Lambert–Eaton Syndrome Sera: Motoneurons Are Preferentially Affected, and L-Type Currents Are Spared

“…The sensitivity to the dihydropyridine antagonist contrasted with control motoneurons, in which micromolar nimodipine blocked 18% of HVA current. L-type current also represents only 6.6% of HVA calcium current in rat hypoglassal motoneurons (Umemiya and Berger, 1994). Additionally, 5 M -CTx MVIIC, which blocks several types of HVA calcium channels including N, P, and Q (Hillyard et al, 1992;Randall and Tsien, 1995), had little effect on the motoneuronal current spared by LES antibodies, whereas it blocked a large fraction of HVA current (70%) in control motoneurons.…”

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

“…T-type channels can cause robust increases in intracellular Ca 2ϩ , especially in proximal dendrites (294,460). Calcium and voltage synergistically open Ca 2ϩ -activated K ϩ channels, which contribute to spike repolarization and afterhyperpolarizations (40,244,416). In addition to transient increases in intracellular Ca 2ϩ , T-type window currents may play an important role in slower increases in basal Ca 2ϩ .…”

Amyloid β Protein Potentiates Ca2+ Influx Through L‐Type Voltage‐Sensitive Ca2+ Channels: A Possible Involvement of Free Radicals

“…The procedures for whole-cell recordings were peifoinsed as previously described (Umemiya and Berger, 1994). Hippocampal pyramidal neurons were visually identified by Nomarski optics.…”