TTX-sensitive Na+ channels and Ca2+ channels of the L- and N-type underlie the inward current in acutely dispersed coeliac-mesenteric ganglia neurons of adult rats.
Inward membrane currents of sympathetic neurons acutely dispersed from coeliac-superior mesenteric ganglia (C-SMG) of adult rats were characterized using the whole-cell variant of the patch-clamp technique. Current-clamp studies indicated that C-SMG neurons retained electrical properties similar to intact ganglia. Voltage-clamp studies designed to isolate Na+ currents revealed that tetrodotoxin (TTX, 1 microM) completely inhibited the large transient inward current. Half activation potential (Vh) and slope factor (K) were -26.8 mV and 6.1 mV, respectively. Inactivation parameters for Vh and K were -65 mV and 8.2 mV, respectively. Voltage-clamp studies also revealed a high-voltage-activated sustained inward Ca2+ current which was blocked by the removal of external Ca2+ or the presence of Cd2+ (0.1 mM). The dihydropyridine agonist, (+)202-791 (1 microM), caused a small increase (20%) in the amplitude of the Ca2+ current at more negative potentials and markedly prolonged the tail currents. omega-Conotoxin GIVA (omega, CgTX, 15 microM) caused a 66% inhibition of the high-voltage-activated Ca2+ current amplitude. Norepinephrine (1 microM) caused a 49% reduction in the peak Ca2+ current. This study is the first demonstration that dispersed C-SMG neurons from adult rats retain electrical characteristics similar to intact ganglia. A TTX-sensitive Na+ current as well as a high voltage-activated sustained Ca2+ current underlie the inward current in C-SMG neurons. The macroscopic Ca2+ current is composed of a small dihydropyridine-sensitive (L-type current) and a large omega-CgTx-sensitive (N-type current) component.(ABSTRACT TRUNCATED AT 250 WORDS)
Carrier
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Department of Pharmacology and Toxicology, Medical College of Georgia, Augusta 30912.
Ikeda
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D000200:Action Potentials; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D004095:Dihydropyridines / Q000494:pharmacology; D005728:Ganglia, Sympathetic / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D015640:Ion Channel Gating; D008297:Male; D008643:Mesentery / Q000294:innervation; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D013779:Tetrodotoxin / Q000494:pharmacology*
D015220:Calcium Channels; D004095:Dihydropyridines; D015222:Sodium Channels; D013779:Tetrodotoxin; C038806:1,4-dihydropyridine; D012964:Sodium; D009638:Norepinephrine