Actions of substance P on membrane potential and ionic currents in guinea pig stellate ganglion neurons

Abstract

Neuropeptides are known to modulate the excitability of mammalian sympathetic neurons by their actions on various types of K+ and Ca2+ channels. We used whole cell patch-clamp recording methods to study the actions of substance P (SP) on dissociated adult guinea pig stellate ganglion (SG) neurons. Under current-clamp conditions, SG neurons exhibited overshooting action potentials followed by afterhyperpolarizations (AHP). The K+ channel blocker tetraethylammonium (1 mM), the Ca2+ channel blocker Cd2+ (0.1–0.2 mM), and SP (500 nM) depolarized SG neurons, decreased the AHP amplitude, and increased the action potential duration. In the presence of Cd2+, the effect of SP on membrane potential and AHP was reduced. Under voltage-clamp conditions, several different K+ currents were observed, including a transient outward K+ conductance and a delayed rectifier outward K+ current ( I K) consisting of Ca2+-sensitive [ I K(Ca)] and Ca2+-insensitive components. SP (500 nM) inhibited I K. Pretreatment with Cd2+ (20–200 μM) or the high-voltage-activated Ca2+ channel blocker ω-conotoxin (10 μM) blocked SP’s inhibitory effects on I K. This suggests that SP reduces I K primarily through the inhibition of I K(Ca) and that this may occur, in part, via a reduction of Ca2+ influx through voltage-dependent Ca2+ channels. SP’s actions on I K were mediated by a pertussis toxin-insensitive G protein(s) coupled to NK1 tachykinin receptors. Furthermore, we have confirmed that 500 nM SP reduced an inward Cd2+- and ω-conotoxin-sensitive Ba2+ current in SG neurons. Thus the actions of SP on I K(Ca) may be due in part to a reduction in Ca2+influx occurring via N-type Ca2+channels. This study presents the first description of ionic currents in mammalian SG neurons and demonstrates that SP may modulate excitability in SG neurons via inhibitory actions on K+ and Ca2+ currents.

Exocytotic release of ATP and activation of P2X receptors in dissociated guinea pig stellate neurons

“…Successfully patched cells were held at Ϫ60 mV, a value of membrane potential near the reported resting membrane potential of guinea pig sympathetic neurons (13,24). Membrane currents were activated by 500-ms depolarizing voltage steps from the holding potential to 0 mV.…”

Extracellular K+ and Opening of Voltage-Gated Potassium Channels Activate T Cell Integrin Function

“…Can the inhibitory effect of Sub P on T cell adhesion be explained, at least in part, by the blocking of Kv1.3 channels? To answer this question, we tested, by electrophysiological techniques, whether Sub P, in a similar manner to its primary action on neurons 27, reduces the T cell membrane voltage-dependent [K + ] conductance. Whole-cell membrane currents were recorded from normal human T cells, in the presence of Sub P, using the voltage-clamp technique 17.…”

Substance P Preferentially Inhibits Large Conductance Nicotinic ACh Receptor Channels in Rat Intracardiac Ganglion Neurons

“…Although SP has been reported to directly modify other membrane conductances in mammalian autonomic neurons, such as inhibiting N-type Ca 2ϩ channel currents in rat sympathetic neurons (Shapiro and Hille 1993) and decreasing K ϩ permeability in neonatal rat sympathetic neurons (Dun and Mo 1988) and adult guinea pig celiac (Vanner et al 1993) and stellate ganglion neurons (Gilbert et al 1998), such effects of SP were not observed in rat parasympathetic intracardiac neurons. SP also failed to alter muscarinic ACh-sensitive K ϩ currents, in contrast to findings in frog sympathetic neurons where SP inhibits the M-current (see Brown 1988) and did not activate a nonspecific cation conductance as has been reported in guinea pig intracardiac ganglion neurons (Hardwick et al 1997).…”