Depolarization of rat isolated superior cervical ganglia mediated by beta 2-adrenoceptors.

Abstract

Depolarizations of freshly-dissected isolated superior cervical ganglia of the rat were recorded extracellularly. The following sympathomimetic amines (in order of decreasing potency) produced depolarizations of up to 0.4 mV: isoprenaline, salbutamol, adrenaline, noradrenaline. Depolarizations were lost after overnight storage, leaving only hyperpolarizing responses. Depolarizations by isoprenaline were antagonized by (-)-propranolol (pA2 8.94 +/- 0.15), (+/-)-butoxamine (pA2 7.36 +/- 0.12) and (+/-)-practolol (pA2 5.14 +/- 0.13). They were not blocked by phentolamine (1 microM) or phenoxybenzamine (1 microM). Isoprenaline and salbutamol were antagonized with equal facility by practolol or butoxamine. In concentrations producing ganglionic depolarization, these compounds also produced a smaller depolarization of presynaptic elements in the ganglion, but not preganglionic trunk fibres. Presynaptic depolarization was blocked by 100 nM propranolol but not by 1 microM phentolamine. Isoprenaline and salbutamol increased the amplitude of the compound ganglionic action potential recorded following single preganglionic nerve stimuli when transmission had been rendered submaximal by adjusting the Ca/Mg ratio, but not in normal solution. Isoprenaline (0.1 microM) also increased the amount of [3H]-acetylcholine released by preganglionic stimulation in low Ca/high Mg solution. It is concluded that facilitatory adrenoceptors are present on pre- and postsynaptic elements in rat superior cervical ganglia, which resembles the 'beta 2' subclass of beta-receptors.