Actions of endothelin-1 on cultured rat renomedullary interstitial cells are modulated by nitric oxide.

1. Cultured renomedullary interstitial cells (RMIC) isolated from 4-week-old Sprague-Dawley rat kidneys possess ETA receptors, as identified by reverse transcription-polymerase chain reaction (RT-PCR). 2. Treatment with endothelin (ET)-1 (10(-6) mol/L) increases the intracellular inositol 1,4,5-trisphosphate concentrations within 10 s and intracellular calcium concentrations after 7 s. 3. Endothelin-1 (10(-7) and 10(-10) mol/L) induced increases in intracellular cAMP concentrations, but only in the presence of N omega-nitro-L-arginine, a nitric oxide synthase (NOS) inhibitor. Addition of ET-1 (10(-10) mol/L) to the RMIC culture led to increases in intracellular cGMP concentrations through activation of NOS. 4. In the presence of ET-1 (10(-7) and 10(-10) mol/L) and during NOS inhibition, RMIC responded with increased cell proliferation and extracellular matrix (ECM) synthesis. These responses were abolished by BQ-123 (10(-6) mol/L), suggesting mediation via the ETA receptor subtype. The proliferative effect of ET-1 was also abolished by atrial natriuretic peptide (10(-6) mol/L). 5. The present study provides evidence that binding of ET-1 to ETA receptors on RMIC activates several intracellular second messenger systems that mediate cell proliferation and ECM synthesis. 6. These results also highlight an important interaction between ET-1 and nitric oxide in the control of RMIC function.