KINETICS OF NORADRENALINE RELEASED BY SYMPATHETIC-NERVES

At the skeletal neuromuscular junction the released neurotransmitter, acetylcholine, is eliminated within some milliseconds.7 This time cour se is known with great precision through the electrical response of ta rget cells.7 At the sympathetic neuroeffector junction the fast electr ical response is not mediated by noradrenatine but by a cotransmitter: ATP.3,11,12 The slow electrical response and the slow component of sm ooth muscle contraction are principally mediated by noradrenaline.3,11 ,12 These responses are two orders of magnitude slower than the electr ical response to ATP.1-3, 10-12 Therefore, great uncertainty remains r egarding the kinetics of noradrenaline appearance and elimination. Her e, the local noradrenaline concentration at the surface of the isolate d rat tail artery was electrochemically monitored in real time using a carbon fibre electrode. We have shown that the time course of the neu rogenically released noradrenaline is at least one order of magnitude faster than the resulting contraction. The kinetics of noradrenaline i nactivation by neuronal reuptake were also precisely measured.