P2x1 Receptor Blockade Inhibits Pressure-Induced Afferent Arteriolar Autoregulatory Behavior.
P2X1 receptors are heavily expressed along the preglomerular vasculature but not on efferent arterioles. P2 receptor activation has been implicated in mediating afferent arteriolar (AA) autoregulatory behavior; however, the receptor subtype responsible remains unknown. This study was performed to test the hypothesis that selective blockade of P2X1 receptors with the novel P2X1 receptor antagonist, NF-279, will inhibit pressure-mediated AA autoregulatory responses. Kidneys from enalaprilat treated (2mg, iv), anesthetized rats were prepared for videomicroscopy experiments using the in vitro blood perfused juxtamedullary nephron technique. Autoregulatory behavior was assessed in response to step increases in perfusion pressure (PP) from 100mmHg to 130 and 160mmHg while AA diameter was continuously monitored. Autoregulatory responses were measured under control (Con) conditions and during P2X1 receptor blockade with NF-279. Time controls have verified that duplicate autoregulatory maneuvers yield similar decreases in AA diameter. During the control period, AA diameter decreased significantly from 20.8 ± 0.8 to 17.3 ± 0.5 (83% of Con) and 14.7 ± 0.7μm (71% of Con) at PP of 100, 130 and 160mmHg, respectively (P<0.05; n=5). During the ensuing recovery period, AA diameter returned to control values (20.6 ± 1.2μm). After the recovery period, 20μM NF-279 was administered via the superfusate. In the presence of NF-279, AA diameter remained stable at 20.6 ± 1.3μm during perfusion at 100mmHg and did not change when PP was increased. AA diameter averaged 20.5 ± 1.3 (98% of Con) and 20.3 ± 1.2μm (97% of Con) at PP of 130 and 160mmHg, respectively. NF-279 abolished the sustained AA response to the P2X1 agonist, α, β-methylene ATP (1μM; P<0.05; n=5), but did not alter the AA response to the A1 receptor agonist, cyclopentyl adenosine (1nM; n=6) or to 1nM Ang II (n=4). These data support our previous observations implicating ATP-induced P2 receptor activation in mediating AA autoregulatory behavior. More importantly, these data provide new and compelling evidence identifying the P2X1 receptor as the specific receptor subtype responsible for AA autoregulatory behavior.