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Purinergic and Adrenergic Ca 2+ Transients during Neurogenic Contractions of Rat Mesenteric Small Arteries
Author(s) -
Lamont Christine,
Vainorius Enrikas,
Wier W. Gil
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.043380
Subject(s) - contraction (grammar) , prazosin , mesenteric arteries , chemistry , isometric exercise , stimulation , medicine , myograph , purinergic receptor , endocrinology , biophysics , anatomy , antagonist , receptor , artery , biology
Contraction of small arteries is regulated by the sympathetic nervous system, but the Ca 2+ transients during neurally stimulated contraction of intact small arteries have not yet been recorded. We loaded rat mesenteric small arteries with the fluorescent Ca 2+ indicator fluo‐4 and mounted them in a myograph that permitted simultaneous (i) high‐speed confocal imaging of fluorescence from individual smooth muscle cells, (ii) electrical stimulation of perivascular nerves, and (iii) recording of isometric tension. Sympathetic neuromuscular transmission was achieved by electrical field stimulation (EFS) (frequency, 10 Hz; pulse voltage, 40 V; pulse duration, 0.2 ms) in the presence of capsaicin and scopolamine (to inhibit ‘sensory’ and cholinergic nerves, respectively). During the first 20 s of EFS, force rose to a small peak and then declined. During this time, junctional Ca 2+ transients (jCaTs) were present at relatively high frequency. We have previously attributed jCaTs to influx of Ca 2+ through post‐junctional P2X receptors activated by ATP. Propagating asynchronous Ca 2+ waves, previously associated with bath‐applied α 1 ‐adrenoceptor agonists, were not initially present. During the next 2.5 min of EFS, force rose slowly, and asynchronous propagating Ca 2+ waves appeared. The selective α 1 ‐adrenoceptor antagonist prazosin abolished both the slowly developing contraction and the Ca 2+ waves, but reduced the initial transient contraction by only ∼25 %. During 3 min of EFS in prazosin, the frequency of jCaTs declined markedly; at sites at which at least one jCaT occurred, the average probability of a jCaT was 0.008 ± 0.002 pulse −1 in the first 20 s and 0.0007 ± 0.0002 pulse −1 in the last 20 s. We suggest that (i) ATP released from sympathetic varicosities activates the initial, transient, contraction and the activator Ca 2+ is derived largely from jCaTs, and (ii) sympathetically released noradrenaline (NA) activates the later, major contraction through mechanisms involving α 1 ‐adrenoceptors and which are associated with propagating Ca 2+ waves.