Mechanism of Diuresis and Natriuresis by Cannabinoids: Evidence for Inhibition of Na⁺-K⁺-ATPase in Mouse Kidney Thick Ascending Limb Tubules

Abstract

The endocannabinoid, anandamide (AEA), stimulates cannabinoid receptors (CBR) and is enriched in the kidney, especially the renal medulla. AEA infused into the renal outer medulla of mice stimulates urine flow rate and salt excretion. Here we show that these effects are blocked by the CBR Type I (CB1) inverse agonist, rimonabant. Immunohistochemical analysis demonstrated the presence of CB1 in thick ascending limb (TAL) tubules. Western immunoblotting demonstrated the presence of CB1 (52 KDa) in the cortex and outer medulla of mouse kidney. The effect of direct (CP55940 (CP) or AEA) or indirect (fatty acyl amide hydrolase (FAAH) inhibitor, PF3845 (PF)) cannabinoidimetics on Na + transport in isolated mouse TAL tubules was studied using the Na +-sensitive dye, SBFI-AM. Switching from 0 Na + solution to control Ringers solution (CR) rapidly increased TAL cell [Na + ] i. Addition of CP to CR produced a further elevation, similar in magnitude to that of ouabain, a Na +-K +-ATPase inhibitor. This [Na + ] i-elevating effect of CP was time-dependent, required the presence of Na + in the bathing solution, and was insensitive to Na +-K +-2Clco-transporter (NKCC2) inhibition. Addition of PF to CR elevated [Na + ] i in FAAH wildtype but not FAAH knockout (KO) TALs, whereas the additions of CP and AEA to PF-treated FAAH KO TALs increased [Na + ] i. An interaction between cannabinoidimetics and ouabain (Ou) was observed. Ou produced less increase in [Na + ] i after cannabinoidimetic treatment, whereas cannabinoidimetics had less effect after Ou treatment. It is concluded that cannabinoidimetics, including CP and AEA, inhibit Na + transport in TALs by inhibiting Na + exit via Na +-K +-ATPase.

Cannabinoid Receptor 1 Inhibition in Chronic Kidney Disease: A New Therapeutic Toolbox

“…CB1R may also modulate the Ang II pressor effect by its action on sodium and water balance. As described earlier, CB1R may be involved in the regulation of salt and water balance (46,79,122,(127)(128)(129)(130). Furthermore, Ang II type 1 receptors (AT1) are largely expressed within the kidney.…”

“…However, recent data shown that a peripheral modulation could also be involved (46,79,(127)(128)(129). As mentioned above, several studies confirmed that tubular cells express the main components of ECS, including CB1R and possibly CB2R as well as the enzymes for biosynthesis and degradation of their ligands (74,130). However, not only the physiological role of CB1R in tubular cells, but also the mechanism responsible for an aquaretic and/or diuretic effect of ECS, remain controversial.…”

“…In rat kidneys, the effect of oral THC administration on urine and Na + output was comparable to the thiazide diuretic, hydrochlorothiazide (122). More recently, Ritter et al reported a natriuretic effect of AEA (79,130). They found that AEA infusion into the mouse renal medulla increased both sodium excretion and urine output (79,130).…”

“…More recently, Ritter et al reported a natriuretic effect of AEA (79,130). They found that AEA infusion into the mouse renal medulla increased both sodium excretion and urine output (79,130). The authors initially reported that a non-canonical CB receptor-based mechanism could be involved (79).…”

“…More recently, Ritter et al found that rimonabant also blocked the effects of AEA, suggesting a CB1R-dependent effect of intramedullary AEA on flow rate and natriuresis (130). Using ex vivo experiments on isolated mouse kidney thick ascending limb (TAL) tubule cells, they demonstrated an inhibitory effect of AEA on the Na + /K + -ATPase activity (130). Another team measured oxygen consumption in rat TAL suspensions to monitor the effects of AEA (46).…”