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Department of Physiology and Biophysics, Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4H7
To determine the chemotransduction
characteristics of ventricular sensory neurites associated with nodose
ganglion afferent neurons, various chemicals were applied individually
to epicardial sensory neurites associated with individual afferent
neurons in anesthetized guinea pigs. The following ion
channel-modifying agents were tested: barium chloride, cadmium
chloride, calcium chloride, the chelating agent EGTA, nickel chloride,
potassium chloride, tetraethylammonium chloride, and
veratridine. An acidic solution (pH 6.0) and oxygen-derived
free radicals (H2O2) were tested. The following
chemicals were also tested: adenosine,
- and
-adrenergic
agonists, angiotensin II, bradykinin, calcitonin gene-related peptide
(CGRP), histamine, nicotine, the nitric oxide donor nitroprusside,
substance P, and vasoactive intestinal peptide. A total of 102 cardiac
afferent neurons was identified, of which ~66% were sensitive to
mechanical stimuli applied to their epicardial sensory fields.
Application of individual ion channel-modifying agents to epicardial
sensory fields modified most associated afferent neurons, with barium
chloride affecting each neuron studied. Ventricular sensory neurites
associated with most identified neurons were also responsive to the
other tested chemicals, with hydrogen peroxide, adenosine, angiotensin
II, bradykinin, CGRP, clonidine, and nicotine inducing responses from
at least 75% of the neurons studied. It is concluded that
1) the ventricular sensory neurites associated with nodose
ganglion afferent neurons transduce a much wider variety of chemical
stimuli than considered previously, 2) these sensory neurites employ a variety of membrane ion channels in their
transduction processes in situ, and 3) adrenergic agents
influence on sensory neurites associated with cardiac afferent neurons
suggests the presence of a cardiac feedback mechanism involving local
catecholamine release by adjacent sympathetic efferent postganglionic
nerve terminals.
adenosine; adrenergic; angiotensin II; adenosine 5'-triphosphate; bradykinin; calcitonin gene-related peptide; histamine; H2O2; ion channel modifiers; nicotine; nitric oxide donor; substance P; vasoactive intestinal peptide
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