title: Individual sympathetic varicosities possess different sensitivities to alpha 2 and P2 receptor agonists and antagonists in mouse vas deferens.
abstract: 1. The diversity of alpha(2) and purinergic autoreceptor actions on action potential evoked calcium transients in single varicosities has been investigated using the calcium indicator Oregon Green 488 BAPTA-1. 2. During long trains of impulses (10 Hz for 30 s), the change in calcium concentration in varicosities from its resting level (Delta[Ca(2+)](v)) increased in many varicosities during the first 3 s of stimulation before reaching a plateau. 3. The alpha(2) adrenoceptor agonist clonidine (1 microM) decreased Delta[Ca(2+)](v) by over 40% during short trains (five impulses at 5 Hz) in most varicosities, although some were unaffected. The alpha(2) adrenoceptor antagonist idazoxan (2 microM) increased the Delta[Ca(2+)](v) plateau following long trains in most varicosities. Hence, most varicosities possess alpha(2) adrenoceptors which are activated when noradrenaline accumulates extracellularly. 4. During long trains of impulses, the P(2y)-purinergic receptor agonist 2-methyl-thio-ATP (100 microM) decreased Delta[Ca(2+)](v) plateau by about 50% in most varicosities; alpha,beta-methylene ATP (100 microM) decreased it by about 50% in a minority of varicosities; adenosine (200 microM) had no significant effect. Suramin (100 microM) increased the Delta[Ca(2+)](v) during all stimulus protocols in most varicosities, suggesting that ambient ATP modulates Delta[Ca(2+)](v) responses. The P(2y) receptor antagonist reactive blue (100 microM) affected a minority of varicosities. Given that most varicosities respond to suramin, other P(2) receptor subtypes are probably present. 5. The ATP ectoenzyme antagonist ARL67157 (50 microM) decreased the plateau Delta[Ca(2+)](v) during long trains in complete strings of varicosities but not in others. 6. The present technique indicates that varicosities have diverse autoreceptor utilization.
authors.affiliation: Neurobiology Laboratory, Institute for Biomedical Research, University of Sydney, NSW 2006, Australia.
authors.forename: S C
authors.initials: SC
authors.lastname: O'Connor
authors.forename: K L
authors.initials: KL
authors.lastname: Brain
authors.forename: M R
authors.initials: MR
authors.lastname: Bennett
mesh_terms: D000320:Adrenergic Fibers / Q000187:drug effects / Q000378:metabolism; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004558:Electric Stimulation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D017729:Presynaptic Terminals / Q000187:drug effects* / Q000378:metabolism; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000378:metabolism; D011983:Receptors, Purinergic / Q000187:drug effects* / Q000378:metabolism; D014649:Vas Deferens / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D018341:Receptors, Adrenergic, alpha-2; D011983:Receptors, Purinergic; D002118:Calcium