LAUSR

In Ang II dependent hypertension, the increased afferent arteriolar resistance (AAR) is assumed to be primarily due to the increased intrarenal levels of Ang II activating AT1 receptors. Because the renal interstitial ATP levels increase with increased renal perfusion pressure (RPP), purinergic P2X receptors (P2XR) also influence AAR. However, the interactions between the respective receptors has not been fully established. Accordingly, experiments were performed to test the hypothesis that P2XR and AT1R share post-receptor signaling pathways which allow dominance of P2XR to control AAR. Experiments using the in vitro juxtamedullary nephron preparation allowed direct visualization of afferent arteriolar diameters (AAD). Normotensive and Ang II infused hypertensive rats showed AAD responses to increases in RPP from 100 to 140 mmHg by decreasing AAD by 26% ± 10% and 19% ± 4% demonstrating autoregulation. In kidneys from normotensive rats, superfusion at 100 mmHg RPP with 5 μM ATP induced a rapid vasoconstriction from a control of 14.5 ± 0.9 μm to 11.2 ± 0.7 μm (n=8, P < 0.05). P2X1 receptor inhibition with NF449 (1 μM) increased AAD by 28% ± 7% returning it close to control values (14.0 ± 0.8 μm). P2X7 receptor inhibition with A438079 (1 μM) did not significantly alter the AAD (12.2 ± 0.6 μm), but combined treatment with P2X1R plus P2X7R inhibitors fully returned the AAD to control values (14.8 ± 0.7 μm), reflecting a dominant role of P2X1R in mediating ATP afferent vasoconstriction in normotensive kidneys. In Ang II infused hypertensive rats, at RPP 140 mmHg, treatment with AT1R inhibitor by SML1394 (1 μM) increased AAD by 10% ± 7% (13.44 ± 0.73 μm vs. 12.21 ± 0.63 μm, n=10, P<0.05). Treatment with P2X1R inhibitor increased AAD by 21% ± 14% (14.42 ± 0.51 μm vs. 11.94 ± 1.20 μm, n=5, P<0.05), and treatment with the P2X7R inhibitor also dilated AAD by 15% ± 3% (12.98 ± 0.64 μm vs. 11.26 ± 0.61 μm, n=5, P<0.05) reflecting a greater role of P2X7R in hypertension. Importantly, treatment with P2X1R inhibitor plus P2X7R inhibitor fully restored AAD to control levels (15.00 ± 0.65 μm vs. 12.02 ± 0.70 μm, n=5, P<0.05). The results suggest that in Ang II dependent hypertension, P2X1R, P2X7R and AT1R act through post-receptor converging signaling pathways allowing dominance of P2XR to regulate AAR.