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Modulation of N‐type calcium currents by presynaptic imidazoline receptor activation in rat superior cervical ganglion neurons
Author(s) -
Chung Seungsoo,
Ahn dukcsun,
Kim Young Hwan
Publication year - 2011
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.25.1_supplement.lb494
Subject(s) - rauwolscine , chemistry , endocrinology , medicine , imidazoline receptor , pertussis toxin , agonist , superior cervical ganglion , receptor , antagonist , biology , g protein , prazosin
Presynaptic imidazoline receptors (Ri‐pre) are found in the sympathetic axon terminals of animal and human cardiovascular systems, and they regulate blood pressure by modulating the release of peripheral noradrenaline (NA). The cellular mechanism of Ri‐pre‐induced inhibition of NA release is unknown. We, therefore, investigated the effect of Ri‐pre activation on voltage‐dependent Ca2+ channels in rat superior cervical ganglion (SCG) neurons. Cirazoline (30 μ m), an Ri‐pre agonist as well as an α ‐adrenoceptor (R α ) agonist, decreased Ca2+ currents ( I Ca) by about 50% in a voltage‐dependent manner with prepulse facilitation. In the presence of low‐dose rauwolscine, which blocks the α 2‐adrenoceptor (R α 2), cirazoline still inhibited I Ca by about 30%, but prepulse facilitationwas significantly attenuated. This inhibitory action of cirazoline was almost completely prevented by high‐dose rauwolscine, which blocks Ri‐pre as well as R α 2. In addition, pretreatment with LY320135, another Ri‐pre antagonist, in combination with low‐dose rauwolscine, also blocked the R α 2‐resistant effect of cirazoline. Addition of guanosine‐5_‐ O ‐(2‐thiodiphosphate) to the internal solutions significantly attenuated the action of cirazoline. However, pertussis toxin did not significantly influence the inhibitory effect of cirazoline. Moreover, cirazoline suppressed Mcurrent in SCG neurons cultured overnight. Finally, ω ‐conotoxin ( ω ‐CgTx) GVIA obstructed cirazolineinduced current inhibition, and cirazoline significantly decreased the frequency of action potential firing in a partly reversiblemanner.