Hemin induces active chloride secretion in Caco-2 cells

Abstract

Enterocytes maintain fluid-electrolyte homeostasis by keeping a tight barrier and regulating ion channels. Carbon monoxide (CO), a product of heme degradation, modulates electrolyte transport in kidney and lung epithelium, but its role in regulating intestinal fluid-electrolyte homeostasis has not been studied. The major source of endogenous CO formation comes from the degradation of heme via heme oxygenase. We hypothesized that heme activates electrolyte transport in intestinal epithelial cells. Basolateral hemin treatment increased baseline Caco-2 cell short-circuit currents ( Isc) twofold (control = 1.96 ± 0.14 μA/cm2 vs. hemin = 4.07 ± 0.16 μA/cm2, P < 0.01); apical hemin had no effect. Hemin-induced Isc was caused by Cl− secretion because it was inhibited in Cl−-free medium, with ouabain, 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), or DIDS. Apical electrogenic Na+ channel inhibitor benzamil had no effect on hemin-induced Isc. Hemin did not alter the ability of Caco-2 cells to respond maximally to forskolin, but a soluble guanylate cyclase inhibitor, [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) inhibited the effects of hemin. A CO-releasing molecule, tricarbonyldichlororuthenium II, induced active Cl− secretion that was also inhibited with ODQ. We conclude that hemin induces active Cl− secretion in Caco-2 cells via a cGMP-dependent pathway. These effects are probably the consequence of CO formation. Heme and CO may be important regulators of intestinal fluid-electrolyte homeostasis.

Regulation of Colonic Ion Transport by Gasotransmitters

“…42) A similar induction of Cl Ϫ secretion by a CO donor or pretreatment with heme to stimulate endogenous CO production is already known from the colonic tumor cell line, Caco-2. 43) In these cells, the CO-induced secretion was reduced by an inhibitor of the soluble guanylate cyclase (ODQ; 1H- [1,2,4]oxadiazolo [4,3-a]quinoxalin-1-one), which is consistent with the 'classical' CO signalling pathway. However, CORM-2 induced anion secretion in rat distal colon was neither affected by ODQ nor reduced after pretreatment with an activator of this pathway (YC1; 3-[5Ј-hydroxymethyl-2Ј-furyl]-1-benzylindazole) suggesting an action of CO independent from the stimulation of this enzyme.…”

Physiology and Pathophysiology of Heme

“…With regard to the latter consideration, heme can influence transport activity in other polarized epithelia such as enterocytes (61), and evidence is accumulating that products of heme, generated by HO, such as CO, can alter tubular and hemodynamic function of the kidney.…”

Carbon monoxide-releasing molecules (CO-RMs): vasodilatory, anti-ischaemic and anti-inflammatory activities

“…Arregui et al [18] reported that liberation of CO from CORM-1 has a positive effect on the renal circulation, as treatment of rats with this CO carrier leads to a significant increase in renal blood flow, glomerular filtration rate and urinary cGMP excretion both under basal conditions and after inhibition of haem oxygenase activity [18]. CO-mediated guanylate cyclase and potassium channel activation by CORM-1 and CORM-2 have also been implicated in inhibition of afferent arteriole constriction in the kidney [19], anal sphincter relaxation [20], nonadrenergic non-cholinergic inhibitory neurotransmission in porcine jejunum [21], immunophotoprotection against UV radiation in rat skin [22], modulation of ion transport in human intestinal epithelial cells [23] and vasorelaxation in hypertensive animals following exercise training [24].…”