TTX-sensitive Na+ channels and Ca2+ channels of the Land N-type underlie the inward current in acutely dispersed coeliac-mesenteric ganglia neurons of adult rats

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Abstract
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 μM) completely inhibited the large transient inward current. Half activation potential (V h) and slope factor (K) were −26.8 mV and 6.1 mV, respectively. Inactivation parameters for V h 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 μM), caused a small increase (20%) in the amplitude of the Ca2+ current at more negative potentials and markedly prolonged the tail currents. ω-Conotoxin GIVA (ω, CgTX, 15 μM) caused a 66% inhibition of the high-voltage-activated Ca2+ current amplitude. Norepinephrine (1 μM) 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 dihydropyridinesensitive (L-type current) and a large ω-CgTx-sensitive (N-type current) component. Thus, acutely dispersed CSMG neurons are suitable for examining the biophysical properties and modulation of membrane currents of adult prevertebral sympathetic neurons in normal and diseased states.