Figure 8. Representative raw data tracing of the ATP and null probe response to the α₁-agonist, phenylephrine, and increasing doses of the α₁-antagonist, prazosin.

Phenylephrine caused a large increase in the pA detected by the ATP probe. This response was attenuated by the addition of prazosin at 1.4 μmol l⁻¹ and somewhat attenuated by 14.29 μmol l⁻¹, but high doses of prazosin (142.9 μmol l⁻¹) also attenuated the response of the null probe. Therefore, in subsequent experiments, the dose of prazosin used was 1.4 μmol l⁻¹.