Beta-adrenoceptor-mediated hyperpolarization in lymphatic smooth
muscle of the guinea-pig mesentery.
Vonderweid, Pierre-Yves, and Dirk F. Van Helden.
The Neuroscience Group, Discipline of Human Physiology, Faculty of
Medicine & Health Sciences, University of Newcastle, NSW 2308,
Australia
APStracts 2:0504H, 1995.
Intracellular microelectrode recordings were performed to investigate
the consequences of [beta]-adrenoceptor activation in smooth muscle
of guinea-pig mesenteric lymphatic vessels. Isoproterenol (ISO)
hyperpolarized the membrane with an associated increase in membrane
conductance and decreased the amplitude of spontaneous transient
depolarizations. ISO effects were mimicked by forskolin (FSK),
isobutyl-methyl-xanthine and two cAMP derivatives. ISO and FSK
-induced hyperpolarizations were inhibited by H89, an inhibitor of
cAMP-dependent protein kinase (PKA), increased in K+-free solution,
but not affected by ouabain or by the NO-synthase inhibitor Nw-nitro
L-arginine. They were partially inhibited by 20 mM tetraethylammonium
(40%) or by 2.5 mM 4-aminopyridine (55%). The ISO-induced
hyperpolarization was partially inhibited by iberiotoxin (20 nM) and
charybdotoxin (40 nM), while the FSK-induced hyperpolarization was
less affected. In cells where the ISO-induced hyperpolarization was
decreased by 40 [mu]M BAPTA/AM, the FSK-induced hyperpolarization was
little changed. Our results indicate that in guinea-pig mesenteric
lymphatic vessels, [beta]-adrenoceptor stimulation activates a PKA
-dependent K+-conductance, involving more than one channel type.
Received 10 July 1995; accepted in final form 16 October 1995.
APS Manuscript Number H636-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95