WHOLE-CELL AND PERFORATED-PATCH RECORDINGS OF 4 DISTINCT K+ CURRENTS IN ACUTELY DISPERSED CELIAC-SUPERIOR MESENTERIC GANGLIA NEURONS OF ADULT-RATS

Properties and modulation of outward membrane currents in sympathetic neurons acutely dispersed from coeliac-superior mesenteric ganglia (C-SMG) of adult rats were examined using both the whole-cell variant of the patch-clamp technique and the perforated patch approach. Under voltage-clamp, four distinct outward currents were observed: a transient outward current (I-A), a voltage-dependent sustained outward current consisting of a Ca2+-dependent component (I-KCa) and a Ca2+-insensitive component (I-KV), and a muscarinic agonist-sensitive outward current (I-M). I-A was isolated by digital subtraction, and characterized by very rapid activation at potentials more positive than -60 mV and by fast and complete voltage-dependent inactivation. Half inactivation potential (V-h) and slope factor (K) were -76 mV and 8.3 mV, respectively. I-A was not affected by removal of external Ca2+, 1 mM tetraethylammonium ions, muscarinic agonists, or 8-bromo-cyclic AMP, but was suppressed by 4-aminopyridine (1 mM). Depolarizing pulses from of a holding potential of -50 or - 60 mV to potentials more positive than -25 mV concomitantly activated two, independent sustained outward currents which decayed slowly; one exhibited voltage-dependent activation similar to the delayed rectifier current (I-KV) and the other being triggered by Ca2+ influx into the cell (I-KCa). The addition of tetraethylammonium ions (1 mM) strongly reduced the amplitude of the sustained outward currents. I-M was characterized as a noninactivating time- and voltage-dependent outward current which activated at membrane potentials more positive than -60 mV and slowly turned off when the membrane was hyperpolarized back to -60 mV, and was suppressed by muscarinic agonists. The rank order of potency of the agonists tested was: oxotremorine > muscarine > bethanechol.