Regulation of Dopamine Uptake by Vasoactive Peptides in the Kidney

Abstract

Considering the key role of renal dopamine in tubular sodium handling, we hypothesized that c-type natriuretic peptide (CNP) and Ang-(1-7) may regulate renal dopamine availability in tubular cells, contributing to Na(+), K(+)-ATPase inhibition. Present results show that CNP did not affect either (3)H-dopamine uptake in renal tissue or Na(+), K(+)-ATPase activity; meanwhile, Ang-(1-7) was able to increase (3)H-dopamine uptake and decreased Na(+), K(+)-ATPase activity in renal cortex. Ang-(1-7) and dopamine together decreased further Na(+), K(+)-ATPase activity showing an additive effect on the sodium pump. In addition, hydrocortisone reversed Ang-(1-7)-dopamine overinhibition on the enzyme, suggesting that this inhibition is closely related to Ang-(1-7) stimulation on renal dopamine uptake. Both anantin and cANP (4-23-amide) did not modify CNP effects on (3)H-dopamine uptake by tubular cells. The Mas receptor antagonist, A-779, blocked the increase elicited by Ang-(1-7) on (3)H-dopamine uptake. The stimulatory uptake induced by Ang-(1-7) was even more pronounced in the presence of losartan, suggesting an inhibitory effect of Ang-(1-7) on AT1 receptors on (3)H-dopamine uptake. By increasing dopamine bioavailability in tubular cells, Ang-(1-7) enhances Na(+), K(+)-ATPase activity inhibition, contributing to its natriuretic and diuretic effects.

Figure 1

Effects of increasing concentrations (1 pM–100 nM) of CNP and Ang-(1-7) on ³H-dopamine uptake in experiments carried out in vitro in isolated renal cortex. ³H-dopamine uptake is expressed as dpm/mg ± SEM. ^∗ p < 0.05 compared with control. Number of samples: 8–10.

Figure 2

Effects of 100 nM CNP and 100 nM Ang-(1-7) on the time-course curve of ³H-dopamine uptake in isolated renal cortex samples, between 5 and 45 min. ³H-dopamine uptake is expressed as dpm/mg ± SEM. ^∗ p < 0.01 compared with control. Number of samples: 8–10.

Figure 3

Effects of 100 nM CNP and 100 nM Ang-(1-7) on ³H-dopamine uptake in experiments carried out in vitro in isolated renal cortex and medulla samples. ³H-dopamine uptake is expressed as dpm/mg ± SEM. ^∗ p < 0.05 compared with control. Number of samples: 8–12.

Figure 4

Comparison of different vasoactive peptides effects on ³H-dopamine uptake in experiments carried out in vitro in isolated renal cortex samples. ³H-dopamine uptake is expressed as percentage of uptake respect control group.

Figure 5

Effects of 100 nM CNP in the presence of 100 nM anantin or 100 nM cANP (4-23-amide) on ³H-dopamine uptake in renal cortex. ³H-dopamine uptake is expressed as dpm/mg ± SEM. Number of samples: 8–11.

Figure 6

Effects of 100 nM Ang-(1-7) in the presence of 100 nM A-779 or 100 nM PD123319 or 100 nM losartan on ³H-dopamine uptake in renal cortex. ³H-dopamine uptake is expressed as dpm/mg ± SEM. ^∗ p < 0.05 compared with control. ^∗∗ p < 0.05 compared with Ang-(1-7) or Ang-(1-7) plus PD123319. Number of samples: 8–12.

Figure 7

Effects of CNP, Ang-(1-7), dopamine (DA), and hydrocortisone (HC) on Na⁺, K⁺-ATPase activity, calculated as percentage of Na⁺, K⁺-ATPase activity of control values ± SEM in renal cortex. The experiments were carried out in the absence (control) or in the presence of carbidopa. ^∗ p < 0.01 compared with carbidopa alone; ^∗∗ p < 0.05 compared with Ang-(1-7); ^∗∗∗ p < 0.05 compared with dopamine. Number of samples: 8–11.

Figure 8

Schematic representation of the mechanism by which CNP and Ang-(1-7) ((a) and (b), resp.) could enhance dopamine tubular transport in proximal tubule cells, by stimulation of extraneuronal uptake. OCTs: organic cationic transporters. Black circles: dopamine; gray triangle: CNP. Black square: Ang-(1-7). Full arrows and +: stimulation; full arrows and −: inhibition; dot arrows: no effect; ?: hypothetical mechanism.