Characterization of voltage-dependent calcium currents in mouse motoneurons.
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)
Mynlieff
M
M
Department of Physiology, Colorado State University, Fort Collins 80523.
Beam
K G
KG
D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology; D004594:Electrophysiology; D005260:Female; D051379:Mice; D009046:Motor Neurons / Q000502:physiology*; D009539:Nicotinic Acids / Q000494:pharmacology; D010069:Oxadiazoles; D010456:Peptides, Cyclic / Q000494:pharmacology; D011247:Pregnancy; D009435:Synaptic Transmission / Q000502:physiology; D020960:omega-Conotoxins
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D004095:Dihydropyridines; D009539:Nicotinic Acids; D010069:Oxadiazoles; D010456:Peptides, Cyclic; D020960:omega-Conotoxins; C049834:PN 202-791; C053423:Conus magus toxin; D001464:Barium; D000584:Amiloride; C038806:1,4-dihydropyridine