The vas deferens responds to a single electrical pulse with a biphasic contraction caused by cotransmitters ATP and noradrenaline. Removing Mg2+ (normally 1.2 mM) from the physiological salt solution (PSS) enhances the contraction. This study aimed to determine the effect of Mg2+ concentration on nerve cotransmitter-mediated contractions. Rat vasa deferentia were sequentially bathed in increasing (0, 1.2, 3 mM) or decreasing (3, 1.2, 0 mM) Mg2+ concentrations. At each concentration a single field pulse was applied, and the biphasic contraction recorded. Contractions to exogenous noradrenaline 10 μM and ATP 100 μM were also determined. The biphasic nerve-mediated contraction was elicited by ATP and noradrenaline as NF449 (10 μM) and prazosin (100 nM) completely prevented the respective peaks. Taking the contractions in normal PSS (Mg2+ 1.2 mM) as 100%, lowering Mg2+ to 0 mM enhanced the ATP peak to 170 ± 7% and raising Mg2+ to 3 mM decreased it to 39 ± 3%; the noradrenaline peak was not affected by lowering Mg2+ to 0 mM (97 ± 3%) but was decreased to 63 ± 4% in high Mg2+ (3 mM). Contractions to exogenous ATP, but not noradrenaline, were increased in Mg2+ 0 mM and both were inhibited with Mg2+ 3 mM. Changing Mg2+ concentration affects the contractions elicited by the cotransmitters ATP and noradrenaline. The greatest effects were to potentiate the contraction to ATP in Mg2+ 0 mM and to inhibit the contraction to both ATP and noradrenaline in high Mg2+. Future publications should clearly justify any decision to vary the magnesium concentration from normal (1.2 mM) values.
Keywords: ATP; Adenosine 5′triphosphate (ATP) magnesium salt (PubChem CID: 16218987); Cotransmission; Electrically induced contraction; Magnesium ion; Methoxamine hydrochloride (PubChem CID: 6081); NF449; NF449 octasodium salt (PubChem CID: 6093161); Noradrenaline; Noradrenaline bitartrate salt (PubChem CID: 11957447); Prazosin; Prazosin hydrochloride (PubChem CID: 68546); Vas deferens; ω-Conotoxin GVIA; ω-Conotoxin GVIA (PubChem CID: 16133838).
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