P2X Receptors Inhibit NaCl Absorption in mTAL Independently of Nitric Oxide

Abstract

Activation of basolateral P2X receptors markedly reduces NaCl absorption in mouse medullary thick ascending limb (mTAL). Here we tested the role of nitric oxide (NO) in the ATP-mediated (P2X) transport inhibition. We used isolated, perfused mTALs from mice to electrically measure NaCl absorption. By microelectrodes we determined the transepithelial voltage (Vte) and transepithelial resistance (Rte). Via these two parameters, we calculated the equivalent short circuit current, I'sc as a measure of the transepithelial Na+ absorption. Basolateral ATP (100 μM) acutely induced reversible inhibition of Na+ absorption (24 ± 4%, n = 10). Addition of L-arginine (100 μM) had no apparent effect on the ATP-induced transport inhibition. Acute reduction of extracellular [Ca2+] to either 100 nM or 0 nM by addition of EGTA had no effect on the ATP-induced transport inhibition. In the presence of the NO synthase (NOS) inhibitor L-NAME (100 μM) and/or ODQ to inhibit the guanylyl cyclase, the ATP effect remained unaffected. Increasing the concentration and incubation time for L-NAME (1 mM) still did not reveal any effect on the ATP-mediated transport inhibition. Acute addition of the NO donors SNAP (100 μM) and Spermine NONOate (10 μM) did not alter tubular transport. High concentrations of L-NAME (1 mM) in itself, however, reduced the transepithelial transport significantly. Thus, we find no evidence for nitric oxide (NO) as second messenger for P2X receptor-dependent transport inhibition in mTAL. Moreover, Ca2+ signaling appears not involved in the ATP-mediated effect. It remains undefined how P2X receptors trigger the marked reduction of transport in the TAL.

Extracellular Nucleotides and P2 Receptors in Renal Function

“…P2X4 receptor blockade with PSB12054 in ANG II-infused rats increased afferent and efferent arteriole resistance by 78 and 100%, respectively, leading to 51% reduction in single-nephron GFR (154). The elevated blood pressure may reflect endothelial dysfunction (impaired NO release), as has also been found in P2X4 receptor knockout mice (566), although this model also shows salt sensitivity (107), which is probably NO independent (495).…”

“…Intriguingly, P2Y 2 receptor stimulation, either by increasing tubular fluid flow (72) or direct application of ATP/UTP, also stimulates tubular production of NO (475), and NO reportedly inhibits NaCl absorption in the mTAL (374). However, the main mTAL function, i.e., the absorption of NaCl, remained unaffected by stimulation of P2Y 2 receptors or addition of NO donors (327,328,495). It may be that the mTAL is the source of P2Y 2 receptor-stimulated NO production, but is not its target.…”

“…The situation contrasts sharply with distinct inhibitory NaCl transport effects in TAL after stimulation of P2X receptors (477), more specifically basolateral P2X4 receptors (327) (FIGURE 3B). The underlying P2X receptor-related intracellular signaling events remain unresolved, but are NO independent (495). Serendipitous results found that transport inhibition after P2X receptor stimulation is paralleled by a sizeable intracellular alkalization caused by activation of the apical NHE3 transporter (121).…”

Developments and Opportunities for 3D Bioprinted Organoids

“…On maturation, the kidney cells exhibited a microvascular network with tight junctions and cell polarization ( Figure 3D , E , and F ). In nephrotoxicity tests of mature tissues, the metabolism of renal cells and cellular activity produced greater adverse effects with increasing concentrations of cisplatin[ 44 ]. Bioprinting facilitates the precise control of cell deposition in a 3D space in terms of the speed and scale, which could lead to a significant reduction in variability between batches of constructed kidney organoids and even a breakthrough in scale from millimeters to centimeters.…”

“…(from ref. [ 43 ] licensed under Creative Commons Attribution 4.0 license) and (from[ 44 ] Creative Commons Attribution license).…”