DOPAMINE MODULATES PERIPHERAL PURINERGIC NEUROTRANSMISSION THROUGH MULTIPLE PRESYNAPTIC RECEPTORS: TISSUE-DEPENDENT EFFECTS

Abstract This study investigated the identity of presynaptic receptors involved in dopaminergic modulation of purinergic transmission in peripheral tissues including isolated rat vas deferens and urinary bladder. Isometric muscle twitches were established in the two tissues by low frequency electric field-stimulation (0.05 Hz, 1-ms duration, and supramaximal voltage). Exposure to prazosin, 50 nmol l −1 (vas deferens), or atropine, 3 μmol l −1 (urinary bladder), had no effect on the developed twitches. In contrast, desensitisation of P 2X -purinoceptors by α,β-methylene ATP (α,β-mATP, 30 μmol l −1 ) abolished the twitches in both tissues, confirming their purinergic origin. Dopamine (1.8×10 −7 to 4.2×10 −5 mol l −1 ) reduced the twitch response in a concentration-related manner. Yohimbine (α 2 -adrenoceptor antagonist, 0.3 μmol l −1 ) significantly ( P 2 -dopaminoceptors by domperidone (1 μmol l −1 ) produced significant ( P 2 -adrenergic and/or DA 2 -dopaminergic) involved in mediating dopamine effects is dependent on the tissue under investigation.