Jx. Bao et al., KINETICS OF ATP-MEDIATED AND NORADRENALINE-MEDIATED SYMPATHETIC NEUROMUSCULAR-TRANSMISSION IN RAT TAIL ARTERY, Acta Physiologica Scandinavica, 149(4), 1993, pp. 503-519
Electrophysiological, electrochemical and mechanical recordings were e
mployed to study the kinetics of the release and clearance of adenosin
e 5'-triphosphate (ATP) and noradrenaline (NA) as sympathetic co-trans
mitters and of the neurogenic and nonneurogenic contractions in rat is
olated tail artery. The life-time of ATP and NA released by a single p
ulse or 10 pulses at 50 Hz was brief ( < 100 ms, or < 3 s, respectivel
y); the neurogenic contractile responses occurred largely after the tr
ansmitters had been removed from the extracellular space. The ATP-indu
ced neurogenic contractile responses to a single pulse or 10 pulses at
50 Hz were similar in time-course to the responses to direct muscle s
timulation at low voltage; both seemed to be caused by activation of n
ifedipine-sensitive voltage-gated L-type Ca2+ channels. The alpha(1)-
and alpha(2)-adrenoceptor-mediated components of the NA-induced neurog
enic 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 h
igh-frequency trains. So did the ATP level at the receptors and the AT
P-induced neurogenic contraction. The NA levels and the contractile re
sponses induced via alpha(1)- and alpha(2)-adrenoceptors were much bet
ter maintained during ongoing stimulation at 20 Hz but relaxed rapidly
afterwards, suggesting that nerve activity suppressed, and cessation
of nerve activity reactivated NA clearance.