Calcium current modulation in frog sympathetic neurones: L-current is relatively insensitive to neurotransmitters.
1. Neurotransmitters (noradrenaline, NA; chicken II luteinizing hormone-releasing hormone, LHRH) and activators of G proteins (GTP-gamma-S and AlF3) partially inhibit calcium current in bullfrog sympathetic neruones. Activation of the remaining current is slowed and shifted to more positive voltages. 2. The N-type calcium current appears to be the type modulated, since approximately 90% of peak current is blocked by omega-conotoxin (omega CgTx) and modulation is not affected by nisoldipine. 3. Calcium current at relatively negative voltages (-30 to -50 mV) is resistant to transmitter modulation. The current at such voltages is also resistant to omega CgTx, suggesting that it results from a different type of calcium channel. 4. The omega CgTx-resistant current includes dihydropyridine (DHP)-sensitive and DHP-resistant components. The omega CgTx- and DHP-resistant current is inhibited by transmitter agonist, but the DHP-sensitive (L-type) current is not. 5. In cells dialysed with a low concentration of calcium buffer (0.1 mM-BAPTA), transmitters still inhibit N-current incompletely. However, L-current was partially inhibited (approximately 10%) by LHRH, NA and the muscarinic agonist oxotremorine-M (OXO-M).
Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106.
K S
KS
Elmslie
P J
PJ
Kammermeier
S W
SW
Jones
D000535:Aluminum / Q000494:pharmacology; D017607:Aluminum Compounds; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005459:Fluorides / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D010456:Peptides, Cyclic / Q000494:pharmacology; D011892:Rana catesbeiana; D020866:omega-Conotoxin GVIA
D017607:Aluminum Compounds; D015220:Calcium Channels; D018377:Neurotransmitter Agents; D010456:Peptides, Cyclic; D007987:Gonadotropin-Releasing Hormone; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D020866:omega-Conotoxin GVIA; D000535:Aluminum; D009543:Nifedipine; D005459:Fluorides; D009638:Norepinephrine; C032311:aluminum fluoride