Voltage‐dependent ionic currents in dissociated paratracheal ganglion cells of the rat.

Abstract

SUMMARY1. Conventional whole-cell voltage-clamp technique was used to study the electrophysiological and pharmacological properties of voltage-dependent Na', K+ and Ca21 channels in parasympathetic neurones enzymatically dissociated from the paratracheal ganglia of rat trachea. The voltage-dependent Na+, K+ and Ca2+ currents (INa' IK and ICa) were separated by the use of ion subtraction and pharmacological treatments.2. INa was activated by a step depolarization more positive than -50 mV and fully activated at positive potentials more than + 10 mV. The inactivation phase of INa consisted offast and slow exponential components (Tif and Tis' respectively). The rif and r.i were voltage dependent and decreased with a more positive step pulse.3. The time course for recovery of INa from the complete inactivation exhibited two exponential processes.4. The reversal potential of INa was equal to the Na+ equilibrium potential (ENa) and resembled a simple Na+ electrode depending only on external Na+ concentration.5. Tetrodotoxin (TTX) reduced INa without affecting the current kinetics in a concentration-dependent manner, and the concentration of half-maximal inhibition (IC50) was 6 x 10' M. There was no TTX-resistant component of INa in any of the cells tested.6. Scorpion toxin increased the peak amplitude of INa and prolonged the inactivation phase in a time-and concentration-dependent manner. In the presence of toxin, both ris and the fractional contribution of the slow current component to total INa increased concentration dependently.7. High-threshold (L-type) ICa was activated by a step depolarization more positive than -30 mV and reached a peak at near 0 mV in the external solution with 2-5 mm Ca2+. The current was inactivated to only a small extent (< 10%) during 100 ms of depolarizing step pulse. There was no low-threshold (T-type) ICa in this preparation.8 K. AIBARA, S. EBIHARA AND KY AKAIKE 9. The inactivation process of the L-type ICa was dependent on Ca2+ influxes (ICadependent inactivation).10. Relative maximum peak currents of divalent cations passing through the Ltype Ca2+ channels were in the order of IBa > ICa > ISr.11. Organic and inorganic Ca2+ antagonists blocked the ICa in a concentrationdependent manner. The order of inhibition was wo-conotoxin > flunarizine > nimodipine > D600 > diltiazem > amiloride for organic blockers and La3+ > Cd2+ > Ni2+ > Co2+ for inorganic ones.12. Three types of IK were observed; i.e. an inwardly rectifying current, a delayed outward current ('KD) and a transient outward current ('A) 13. Depolarizing pulses from a holding potential (VH) of -90 mV elicited K+ currents which seemed to suggest the existence of two distinct cell types. The 'A was observed in the majority of cells (44 out of 63 cells). The IKD was elicited in all cells tested.14. 'KD was activated by step pulses more positive than -20 mV, slowly inactivated (T > 1 s) and reduced by adding tetraethylammonium (IC50 was 4 4 mM).15. The IA was characterized by a rapid activation and inactivation. The amplitude o...

Acetylcholine modulation of high‐voltage‐activated calcium channels in the neurones acutely dissociated from rat paratracheal ganglia

“…Neuronal Ca 2+ channels have been shown to be classified into two subtypes including low‐voltage‐activated (LVA) and high‐voltage‐activated (HVA) Ca 2+ channels. However, as previously described (Aibara et al , 1992), the LVA Ca 2+ channel current was not observed in the present preparation (not shown). Therefore, the effects of ACh on HVA 7 Ca evoked by a depolarizing step pulse from a holding potential (V H ) of ‐ 50 mV to + 20 mV were examined.…”

An electrophysiological study of muscarinic and nicotinic receptors of rat paratracheal ganglion neurons and their inhibition by Z‐338

“…The procedure for obtaining dissociated paratracheal ganglion neurons is similar to that described elsewhere (Aibara et al ., 1992; Ishibashi et al ., 2001). Briefly, the paratracheal ganglia were rapidly removed from the trachea of 2‐week‐old Wistar rats under ether anaesthesia, and the rats were subsequently killed by exsanguination.…”

Morphology and electrophysiology of guinea-pig paratracheal neurones

“…Likewise, there is still surprisingly little information about the electrophysiological properties of tracheal ganglion neurones, given the important role of such neurones in the regulation of airway tone and secretion. Electrophysiological investigations have been made of paratracheal neurones of the ferret (Baker et al, 1986;Cameron and Coburn, 1984;Coburn, 1984Coburn, , 1987Coburn and Kalia, 1986), cat (Mitchell et al, 1987) and, most extensively, of the rat (Allen and Burnstock, 1990;Aibara et al, 1992;Reekie and Burnstock, 1992).…”