Figure 3.

Contribution of α₁-adrenergic and P2X purinergic receptors to neurogenic constriction of MA and MV A, effects of PPADS (10 μm) on neurogenic constriction (top) and NA-oxidation current caused by a 20 Hz stimulus train (60 pulses with a 0.3 ms pulse width) in a MA. PPADS blocked the constriction but not the NA oxidation current. B, PPADS did not alter the neurogenic constriction or NA oxidation current in a MV. C, apparent concentration–constriction curves for neurally released NA in MA in the absence and presence of PPADS and prazosin (0.1 μm). Peak NA oxidation currents were measured during stimulus trains (0.2–20 Hz) by converting oxidation currents to apparent NA concentrations using calibrated electrodes. The curve obtained in the presence of PPADS (square symbols) reveals the sensitivity of MA to neurally relased NA. D, experiments similar to ‘C’ except these studies were done in MV. The curve obtained in the presence of PPADS (▪) reveals the sensitivity of MV to neurally relased NA. Prazosin blocked the constriction caused by nerve stimulation in MV but it did not alter the NA oxidation current (not shown). Data are means ±s.e.m.