Kinetics of ATP- and noradrenaline-mediated sympathetic neuromuscular transmission in rat tail artery.
Electrophysiological, electrochemical and mechanical recordings were employed to study the kinetics of the release and clearance of adenosine 5'-triphosphate (ATP) and noradrenaline (NA) as sympathetic co-transmitters and of the neurogenic and non-neurogenic contractions in rat isolated tail artery. The life-time of ATP and NA released by a single pulse or 10 pulses at 50 Hz was brief (< 100 ms, or < 3 s, respectively); the neurogenic contractile responses occurred largely after the transmitters had been removed from the extracellular space. The ATP-induced neurogenic contractile responses to a single pulse or 10 pulses at 50 Hz were similar in time-course to the responses to direct muscle stimulation at low voltage; both seemed to be caused by activation of nifedipine-sensitive voltage-gated L-type Ca2+ channels. The alpha 1- and alpha 2-adrenoceptor-mediated components of the NA-induced neurogenic contractile response to 10 pulses at 50 Hz were more delayed and prolonged and determined by properties of the post-receptor mechanisms. The per pulse release of both ATP and NA faded rapidly during long high-frequency trains. So did the ATP level at the receptors and the ATP-induced neurogenic contraction. The NA levels and the contractile responses induced via alpha 1- and alpha 2-adrenoceptors were much better maintained during ongoing stimulation at 20 Hz but relaxed rapidly afterwards, suggesting that nerve activity suppressed, and cessation of nerve activity reactivated NA clearance.
Bao
J X
JX
Department of Physiology I, Karolinska Institute, Stockholm, Sweden.
Gonon
F
F
Stjärne
L
L
D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001158:Arteries / Q000294:innervation; D004558:Electric Stimulation; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000294:innervation*; D009469:Neuromuscular Junction / Q000502:physiology*; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*; D013623:Tail / Q000098:blood supply; D013997:Time Factors
D000255:Adenosine Triphosphate; D009638:Norepinephrine