Characteristics of the transport of oxalate and other ions across rabbit proximal colon

Abstract

In order to characterize oxalate handling by the P2 segment of the rabbit proximal colon, the fluxes of [¹⁴C]oxalate, ²²Na⁺, and ³⁶Cl⁻ were measured in vitro using conventional short-circuiting techniques. In standard buffer the proximal colon exhibited net secretion of Na⁺ (−2.31±0.64 μequiv cm⁻² h⁻¹), negligible net Cl⁻ transport, and net secretion of oxalate (−12.7±1.6 pmol cm⁻² h⁻¹). Replacement of buffer Na⁺ or Cl⁻ abolished net oxalate secretion, while HCO ⁻₃ -free media revealed a net absorption of oxalate (19.3±4.2 pmol cm⁻² h⁻¹) and stimulated NaCl absorption. Mucosal amiloride and dimethylamiloride (1 mM) significantly reduced the unidirectional fluxes of oxalate and enhanced sodium secretion by decreasing J ^Na_ms . The anion exchange inhibitor 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS; 0.1 mM, both sides) reduced the unidirectional fluxes of oxalate and chloride. Serosal epinephrine (50 μM) stimulated oxalate absorption (21.3±6.3 pmol cm⁻² h⁻¹) and sodium absorption (5.71±1.20 μequiv cm⁻² h⁻¹), whereas dibutyryl-cAMP enhanced oxalate secretion (−43.4±6.9 pmol cm⁻² h⁻¹) and stimulated chloride secretion (−7.27 ±0.64 μequiv cm⁻² h⁻¹). These results indicate that the P2 segment of the proximal colon possesses (a) secretory as well as absorptive capacities, (b) oxalate fluxes that are mediated by pathways involving Na⁺, Cl⁻, HCO ⁻₃ transport and (c) a net oxalate flux that is sensitive to absorptive and secretory stimuli.