TTX-SENSITIVE NA+ CHANNELS AND CA2+ CHANNELS OF THE L-TYPE AND N-TYPE UNDERLIE THE INWARD CURRENT IN ACUTELY DISPERSED CELIAC-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-mu-M) completely inhibited the large transient inward current. Half activation potential (V(h)) and slope factor (K) were - 26.8 mV and 0.1 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-mu-M), 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-mu-M) Caused a 66% inhibition of the high-voltage-activated Ca2+ current amplitude. Norepinephrine (1-mu-M) 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. Thus, acutely dispersed C-SMG neurons are suitable for examining the biophysical properties and modulation of membrane currents of adult prevertebral sympathetic neurons in normal and diseased states.