Oxalate secretion in the rat proximal tubule

Abstract

Simultaneous capillary and luminal microperfusion studies in the proximal convoluted tubule of the rat were performed to examine the transepithelial secretory flux of [14C]oxalate. Increases in the concentration of oxalate in the capillary solution from 0.096 to 4.3 mM resulted in progressively higher rates of oxalate secretion into the lumen. Further increases in the capillary concentration of oxalate indicated a tendency toward a plateau. The inclusion of para-chloromercuribenzoate, sodium cyanide, indanyloxyacetic acid, furosemide, or para-aminohippurate in the capillary solution significantly lowered the secretory flux of oxalate. the addition of probenecid in a concentration of 10(-4) M inhibited oxalate secretion when the oxalate concentration in the capillary solution ranged between 1.1 and 4.3 mM, but did not affect oxalate secretion at higher capillary concentrations of oxalate. These results indicate that oxalate secretion in the rat proximal tubule is an active carrier-mediated process. When considered in conjunction with prior studies, the present investigations suggest the possibility that more than one oxalate secretory system exists in the rat proximal tubule.

Oxalate: From the Environment to Kidney Stones

“…In addition to secreting oxalate, proximal tubules are also sites of limited oxalate reabsorption (135,136), whereas the distal parts of a nephron are not involved in oxalate transport (137). Detailed studies on rat kidney proximal tubules indicated the presence of a low-affinity, high-capacity excretory system for o x a l a t e , w h i c h c a n b e i n h i b i t e d b y pchloromercuribenzoic acid (PCMB), cyanide, indacrinone (MK-196), furosemide, and paminohippurate (PAH) (137,138). However, these and other studies suggested that more than one secretory system, with different affi nities for oxalate, may be responsible for oxalate handling in mammalian kidneys (129, 137, and 138).…”

The liver and kidney expression of sulfate anion transporter sat-1 in rats exhibits male-dominant gender differences

“…The elimination of oxalate from hepatocytes is mediated by sat-1 in the sinusoidal cell membrane, in exchange for sulfate or bicarbonate. Most of the endogenous oxalate is finally eliminated by the kidneys; handling of oxalate in the rat kidneys includes filtration, partial reabsorption, and additional secretion in the proximal convoluted tubules, with the net secretion as the final outcome [19,46]. The secretory processes for oxalate in proximal tubules seem to be mediated by the concerted action of two anion exchangers, e.g., the basolateral sat-1 (Slc26a1) and the apical CFEX.…”

“…The latter transporter functions in multiple exchange modes using oxalate, chloride, formate, sulfate, or bicarbonate as substrates [2,16]. The distal tubule has a minor role in oxalate secretion in rats [19,46] and rabbits [44].…”

Primary and secondary hyperoxaluria: Understanding the enigma

“…Renal oxalate handling comprises glomerular filtration, tubular secretion and tubular reabsorption [14,15] . Glo merular filtration depends on the plasma oxalate levels while tubular transport is mediated by SLC26 family of transport proteins.…”

“…This exchanger also mediates intestinal secretion of oxalate and loss of this exchanger has been shown to promote increased intestinal absorption of oxalate in the small intestine [18,19] . In rat kidney, tubular reabsorption has been demonstrated in the S1 and S2 segments of the proximal tubule [14] which may help decrease the tendency for calcium oxalate supersaturation in the earlier parts of the nephron [3] . Overall, the contribution of tubular secretion in addition to glomerular filtration is critical in regulating plasma oxalate levels as a strong correlation has been demonstrated between high plasma oxalate levels and oxalate secretion [20] .…”