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Calcium current modulation in frog sympathetic neurones: L‐current is relatively insensitive to neurotransmitters.
Author(s) -
Elmslie K S,
Kammermeier P J,
Jones S W
Publication year - 1992
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1992.sp019329
Subject(s) - chemistry , endocrinology , voltage dependent calcium channel , calcium , nisoldipine , bapta , medicine , biophysics , oxotremorine , p type calcium channel , dihydropyridine , agonist , t type calcium channel , biochemistry , biology , receptor , nifedipine , organic chemistry
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).