A, Predicted scheme of inner medullary colleting duct ET-1, acting via the ETB receptor to regulate NO production through a MAPK dependent pathway. B) ETA receptor antagonism with BQ123 does not prevent the ET- 1 (50 nM for 24 h) dependent increase in mIMCD-3 nitrite production (Two-Factor ANOVA: antagonist p = 0.0025, ET-1 treatment P < 0.0001, interaction p = 0.125). C) ETB receptor antagonism with BQ788 blunts the ET-1 (50 nM for 24 h) dependent increase in mIMCD-3 nitrite production (Two-Factor ANOVA: Drug p = 0.007, ET-1 Treatment p < 0.001, interaction p = 0.002). N= 4. * P <0.05 vehicle vs. ET1.