Characterization of voltage-dependent calcium currents in mouse motoneurons

J Neurophysiol. 1992 Jul;68(1):85-92. doi: 10.1152/jn.1992.68.1.85.

Abstract

1. Calcium channel currents were measured with the whole-cell patch clamp technique in cultured, identified mouse motoneurons. Three components of current were operationally defined on the basis of voltage dependence, kinetics, and pharmacology. 2. Test potentials to -50 mV or greater (10 mM external Ca2+) elicited a low-voltage activated T-type current that was transient (decaying to baseline in less than 200 ms) and had a relatively slow time to peak (20-50 ms). A 1-s prepulse to -45 mV produced approximately half-maximal inactivation of this T current. 3. Two high-voltage activated (HVA) components of current (1 transient and 1 sustained) were activated by test potentials to -20 mV or greater (10 mM external Ca2+). A 1-s prepulse to -35 mV produced approximately half-maximal inactivation of the transient component without affecting the sustained component. 4. When Ba2+ was substituted for Ca2+ as the charge carrier, activation of the HVA components was shifted in the hyperpolarizing direction, and the relative amplitude of the transient HVA component was reduced. 5. Amiloride (1-2 mM) caused a reversible, partial block of the T current without affecting the HVA components. 6. The dihydropyridine agonist isopropyl 4-(2,1,3-benzoxadiazol-4-yl)-1,4-dihydro-2,6-dimethyl-5-nitro-3- pyridine-carboxylate [(+)-SDZ 202-791, 100 nM-1 microM)] shifted the activation of the sustained component of HVA current to more negative potentials and increased its maximal amplitude. Additionally, (+)-SDZ 202-791 caused the appearance of a slowed component of tail current.(ABSTRACT TRUNCATED AT 250 WORDS)

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amiloride / pharmacology
  • Animals
  • Barium / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Calcium Channels / physiology*
  • Cells, Cultured
  • Dihydropyridines / pharmacology
  • Electrophysiology
  • Female
  • Mice
  • Motor Neurons / physiology*
  • Nicotinic Acids / pharmacology
  • Oxadiazoles*
  • Peptides, Cyclic / pharmacology
  • Pregnancy
  • Synaptic Transmission / physiology
  • omega-Conotoxins*

Substances

  • Calcium Channel Blockers
  • Calcium Channels
  • Dihydropyridines
  • Nicotinic Acids
  • Oxadiazoles
  • Peptides, Cyclic
  • omega-Conotoxins
  • PN 202-791
  • Conus magus toxin
  • Barium
  • Amiloride
  • 1,4-dihydropyridine