Transient excitatory responses to sustained stimulation of intramural nerves in isolated bovine lymphatic vessels.
Spontaneous isometric contractions were measured in 2 cm segments of bovine mesenteric lymphatics. Field stimulation at 4 Hz was applied for a 20 min period. This caused a threefold increase in contraction frequency initially but the response faded rapidly so that, within 6 min of the beginning of stimulation, contraction frequency had returned to a value which was not significantly different from control. In contrast to the effect on frequency 3H efflux from vessels pre-loaded with [3H]noradrenaline was maintained at a value significantly higher than control for the entire stimulation period. The fade in response to exogenous noradrenaline was similar to that seen with field stimulation but with a slightly slower time course. Vessels desensitized with noradrenaline showed a greatly diminished response to field stimulation but responded normally to other agonists. Increasing the extracellular KCl concentration to 18 mM also caused a threefold increase in contraction frequency but, unlike the response to noradrenaline and field stimulation, this was maintained for the 20 min period during which [K+]o was raised. The results suggest that the adrenoceptors on lymphatic smooth muscle exhibit very rapid homologous desensitization.
McHale
N G
NG
Department of Physiology, Queen's University Belfast.
Allen
J M
JM
McCarron
J G
JG
D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002417:Cattle; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D008208:Lymphatic System / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D009638:Norepinephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000187:drug effects / Q000502:physiology
D011941:Receptors, Adrenergic; D011188:Potassium; D001920:Bradykinin; D009638:Norepinephrine