α2c‐Adrenoceptor‐modulated release of noradrenaline in human right atrium

摘要: 1. The aim of the present study was to characterize presynaptic alpha 2-autoreceptors in human right atrium terms 2A-D system. Segments atrial appendages were preincubated with [3H]-noradrenaline and then superfused presence cocaine stimulated electrically. pEC30% values eight alpha-adrenoceptor antagonists discriminatory power determined. is negative logarithm antagonist concentration that increased stimulation-induced overflow tritium by 30%. For four antagonists, dissociation constant KD determined, addition pEC30%, against overflow-inhibiting effect 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK 14,304) under autoinhibition-free conditions. 2. yielded identical rank orders affinity (rauwolscine > WB 4101 phentolamine prazosin) suggesting both released noradrenaline exogenous agonist UK 14,304 activated same receptor inhibit release. 3. obtained correlated significantly their values, reported literature, at 2C-autoreceptors kidney (r = 0.817; slope regression line 1.03). No significant correlation between autoreceptors pKD previously characterized 2A-autoreceptors rabbit 2D-autoreceptors rat, mouse guinea-pig tissues. 4. Comparison native 2 binding sites cells or tissues express a single subtype only, membranes COS transfected genes confirms 2C character autoreceptors: correlations exclusively sites. 5. Ratios computed for genes. autoreceptor ratios corresponded well respective (maximal three fold deviation) but were, part, markedly different from calculated 2A 2B (up 166 deviation). This outcome supports designation autoreceptors. 6. In conclusion, are 2C. this they agree kidney. classification possibly separates, general, those lagomorph (rabbit) rodent (rat, mouse, guinea pig) species have been proposed be predominantly 2D.