A fast transient outward current in the rat sympathetic neurone studied under voltage‐clamp conditions.

Abstract

SUMMARY1. Post-ganglionic neurones of the isolated rat superior cervical ganglion were voltage clamped at 37 0C using separate intracellular voltage and current micro-electrodes.2. Control experiments in current clamp suggested that the neurone is electrotonically compact, the soma and the proximal dendritic membranes being under good spatial voltage uniformity.3. Depolarizing voltage steps from membrane potentials near -50 mV evoked: (i) a voltage-dependent inward Na+ current, (ii) an inward Ca2+ current, (iii) a voltage-dependent outward K+ current, (iv) a Ca2+-activated K+ outward current.4. Depolarizations from holding potentials more negative than -60 mV elicited, besides the currents mentioned above, a fast transient outward current IA which peaked in 1-2 5 ms and then decayed to zero following an exponential time course. 5. The IA current was shown to be primarily, if not exclusively, carried by K+. It was unaffected by removal of external Ca2+ or addition of Cd2+ and was weakly blocked by tetraethylammonium ions and partially by 4-aminopyridine.6. The IA current showed a linear instantaneous current-voltage relationship. Its activation ranged from -60 to 0 mV with a mid-point at -30 mV. The A conductance could be described in terms of a simple Boltzmann distribution for a single gating particle with a valency of + 3.7. Both the development and removal of inactivation followed a single exponential time course with a voltage-dependent time constant which was large near the resting potential (42 ms at -70 mV) and small (11 ms) near -100 and -40 mV.8. Steady-state inactivation h. ranged from -100 to -50 mV, with a mid-point at -78 mV, suggesting that approximately 50 % of the IA channels are available at the physiological resting potential.9. Action potentials elicited from various holding potentials showed maximal repolarization rates dependent on the holding potential itself. This voltage dependence was found to be in reasonably good agreement with that of h. curve.

Elimination of the Fast Transient in Superior Cervical Ganglion Neurons with Expression of KV4.2W362F: Molecular Dissection ofIA

“…Two K ϩ currents with similar decay values have been described previously in rat sympathetic neurons and were assumed to reflect the expression of distinct K ϩ channels (McFarlane and Cooper, 1992). The rapidly inactivating current has been referred to as I A , or I Af (Freshi, 1983;Galvan and Sedlmeir, 1984;Belluzzi et al, 1985a;Nerbonne et al, 1986;McFarlane and Cooper, 1992;Wang and McKinnon, 1995), and the slowly inactivating current has been given various names, including I K (Galvan and Sedlmeir, 1984;Belluzzi et al, 1985b;Nerbonne and Gurney, 1989) and I A,slow (McFarlane and Cooper, 1992). The very slowly decaying current component ( decay ϭ 2560 Ϯ 187 msec) is referred to here as I K to emphasize the slow inactivation kinetics and to distinguish this conductance pathway from I As (see below).…”

Block of potassium currents in rat isolated sympathetic neurones by tricyclic antidepressants and structurally related compounds

“…Effect of tricyclic compounds on transient and sustained components of K+ current As stated in the introduction, it was of interest to compare the effects of these compounds on the transient K+ current in SCG neurones, IA (Belluzzi et al, 1985a) with those on IKV- Figure 6a illustrates a protocol which elicits both IA and IKV (protocol 2, see methods). The peak current measured within 10 ms of the step to 0 mV was 2537 ± 226 pA (n = 30).…”

Activation and inactivation of the bursting potassium channel from fused Torpedo synaptosomes.

“…In this aspect it is similar to other fast activating A-channels such as the Shaker A-type potassium channel in Drosophila muscle , the fast transient potassium currents in adult and neonate rat nodose sensory neurones (Cooper & Shrier, 1985;McFarlane & Cooper, 1991), the rat sympathetic neurones (Belluzzi, Sacchi & Wanke, 1985) and the rat thalamic relay neurones (Huguenard, Coulter & Prince, 1991). It is substantially faster than the transient potassium current found in the neurohypophysial nerve terminals of the rat (Thorn, Wang & Lemos, 1991) and in the hippocampal CA3 neurones (Gustafsson, Galvan, Grafe & Wigstr6m, 1982).…”