Mechanisms of oxalate absorption and secretion across the rabbit distal colon |
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Authors: | Marguerite Hatch Robert W. Freel N. D. Vaziri |
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Affiliation: | (1) Division of Nephrology, Med Sci 1, C380, Department of Medicine, University of California at Irvine, 92717 Irvine, CA, USA |
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Abstract: | To further evaluate the mechanisms of oxalate (Ox2–) transport in the intestine the following studies were performed using isolated, short-circuited segments of the rabbit distal colon (DC). In control buffer, the DC absorbed Ox2– (net Ox2– flux, JNetOx=5.4±0.7 pmol · cm–2 · h–1). Replacement of Na+ with N-methyl-d-glucamine (NMDG+) abolished Ox2– absorption by decreasing mucosal to serosal Ox2– flux (JmsOx), without affecting Cl– transport, while gluconate substitution for Cl– did not affect JNetOxor net Na+ flux (JNetNa). Addition of Na+ to the serosal side of tissues bathed by NMDG+ buffer increased JmsOx40% without altering mucosal to serosal Cl– flux (JmsCl). Serosal amiloride or dimethyl amiloride (10–3 M) abolished JNetOxby decreasing JmsOx, it increased serosal to muscosal Cl– flux (JsmCl) and it gradually inhibited short-circuit current (Isc). Mucosal amiloride (10–4 M) abolished Isc but had no effect on Ox2– or Cl– fluxes. Serosal 4,4 -diisothiocyanatostilbene-2,2 -disulfonic acid (DIDS, 10–6 M) reduced JmsOxby 20% and JNetOxby 43% without affecting JmsClor JNetCl. Dibutyryl cyclic adenosine monophosphate (dB-cAMP, 5×10–4 M, both sides) stimulated Ox2– secretion (JNetOx= –12.6±3.3 pmol · cm–2 · h–1). The dB-cAMP-induced secretion of Ox2– and Cl– were fully abolished by serosal furosemide (10–4 M) and partially inhibited (35%) by 5×10–4 M mucosal NPPB [5-nitro-2-(3-phenylpropylamino)-benzoic acid], a putative Cl– channel blocker. It is proposed that: (1) basal absorption of Ox2–, but not Cl–, is dependent upon a previously undescribed basolateral Na+-H+ exchanger that may be coupled to a DIDS-sensitive, basolateral anion exchange system that mediates Ox2– flux; (2) the DC secretes Ox2– in response to dB-cAMP by a mechanism that is indistinguishable from the pathway for Cl– secretion. |
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Keywords: | Sodium Chloride cAMP DIDS Furosemide NPPB Amiloride Na+-H+ exchange Anion exchange Basolateral membrane |
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