ISSN:
1432-1912
Keywords:
Chick sympathetic neurons
;
Ca2+ currents
;
α2-adrenoceptors
;
Patch clamp
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary In order to gain insight into the mechanism of the autoinhibition of noradrenaline release, the present study explores the effects of substances acting at various adrenoceptor-subtypes on voltage-activated Ca 2+ currents. Experiments were carried out on cultured embryonic chick sympathetic neurons using the patch clamp technique. Ca2+ currents associated with a (fully activating) depolarizing 150 ms voltage step to 0 mV were reduced by noradrenaline and the two a2-adrenoceptor agonists UK 14,304 and clonidine, predominantly during the early phase of activation. We quantified these effects by measuring Ca2+ current amplitudes in the absence and presence of substances 10 ms after the beginning of the depolarization. Noradrenaline effects were maximal at 5 µmol/l, causing a 28% depression of the current. Half-maximal effects (IC50) were apparent at 0.7 µmol/l. UK 14,304 was equipotent to noradrenaline (IC50: 0.5 µmol/l; maximal effect: 26% depression). Clonidine, while active in the same range of concentration (IC50: 0.6 µmol/l), had a smaller maximal effect (20% depression). Methoxamine and isoprenaline, on the other hand, did not significantly reduce the Ca 2+ current at 10 µmol/l. The noradrenaline-induced inhibition was attenuated by yohimbine (1 µmol/I). Neither prazosin (1 µmol/l) nor propranolol (1 µmol/l) interfered with the effect of noradrenaline. These results indicate a reduction of Ca 2+ influx via α2-adrenoceptors and suggest that the autoreceptor-mediated inhibition of transmitter release in embryonic chick sympathetic neurons operates through the modulation of Ca2+ channels.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00183015
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