I. Muramatsu et al., EVIDENCE FOR SYMPATHETIC, PURINERGIC TRANSMISSION IN THE IRIS DILATORMUSCLE OF THE RABBIT, Japanese Journal of Pharmacology, 66(2), 1994, pp. 191-193
Electrical transmural stimulation of isolated iris dilator muscle of t
he rabbit produced a transient contraction that consisted of adrenergi
c and nonadrenergic components. In contrast to the adrenergic componen
t, the nonadrenergic component was resistant to prazosin and other adr
enoceptor antagonists. However, both components were completely blocke
d by guanethidine or tetrodotoxin. Among some tested compounds includi
ng neuropeptide Y, both ATP and 2-methylthio ATP produced a transient
contraction in the dilator muscle and the sustained treatment with eac
h markedly attenuated the nonadrenergic responses to electrical stimul
ation and to ATP. Suramin had no effect on and alpha,beta-methylene AT
P potentiated the responses to electrical stimulation and to ATP. Thes
e results suggest that the nonadrenergic contraction induced by electr
ical transmural stimulation is a sympathetic purinergic response that
may be mediated through unique purinoceptors.