Substrate oxidation by isolated ovine enterocytes is increased by phlorizin-induced glucosuria

Intestinal cells harvested from wethers injected with phlorizin were utilized to determine the effects of decreased glucose availability on glucose, glutamine, and butyrate oxidation by ovine intestinal cells. Phlorizin injection increased (P = 0.002) conversion of substrates to CO2 by isolated enterocytes but not by colonocytes (P = 0.098). Key words: Enterocytes, colonocytes, ruminant, glucose

Na+/K+ATPase activity inhibition and isoform-specific translocation of protein kinase C following angiotensin II administration in isolated eel enterocytes

In the eel, angiotensin II (Ang II) has a role at the level of both gill chloride and kidney tubular cells, regulating sodium balance and therefore osmoregulation. The present study extends these findings to another important osmoregulatory organ - the intestine. Enterocytes were obtained from sea-water (SW)-acclimated eels to investigate the role of Ang II on the intestinal Na+/K+ATPase activity, because in SW-acclimated animals the intestine represents an important site of water and NaCl transport from the mucosal to the serosal side. This paper demonstrates that isolated enterocytes stimulated with increasing Ang II concentrations (0.01-100 nM) showed a dose-dependent inhibition of the Na+/K+ATPase activity. The threshold decrease was at 0.01 nM Ang II; it reached a maximum at 10 nM (81.5% inhibition) and did not decrease further with the use of higher hormone doses. These hormonal effects were blocked by a specific competitive antagonist of the AT1 receptor subtype, DuP-753 (100% inhibition at 10 microM), indicating that these effects are mediated by an AT1-like receptor. Isolated enterocytes stimulated with 10 nM Ang II showed a transient increase in intracellular calcium ([Ca2+]i), followed by a lower sustained phase. Removal of extracellular Ca2+ did not reduce the initial transient response and completely abolished the plateau phase. The inhibition of the Na+/K+ATPase activity was dependent on protein kinase C (PKC) activation since PKC antagonists (calphostin C and staurosporine) abolished the inhibitory effect of Ang II, and the PKC activator phorbol 12-myristate 13-acetate reduced transporter activity. Western blot analysis with antibodies to PKC alpha, beta I, beta II, gamma, delta, epsilon, iota, eta and zeta isoforms showed that eel enterocytes expressed the conventional isoforms (alpha and beta I), the novel isoforms (delta and eta) and the atypical isoforms (zeta and iota). Ang II stimulated the translocation from the cytosol to the plasma membrane of PKC alpha, PKC delta and PKC eta isoforms. In conclusion, our results suggest that Ang II modulates intestinal Na+/K+ATPase in SW-acclimated eels via calcium mobilization and PKC activation.

Acute increase, stimulated by prostaglandin E2, in glucose absorption via the sodium dependent glucose transporter-1 in rat intestine

BACKGROUND/AIMSAcute stimulation by cAMP of the sodium dependent glucose cotransporter SGLT1 has previously been shown. As prostaglandin E2(PGE2) increases intracellular cAMP concentrations via its receptor subtypes EP2R and EP4R, it was investigated whether PGE2 could enhance intestinal glucose absorption.METHODSThe action of PGE2 on carbohydrate absorption in the ex situ perfused rat small intestine and on 3-O-[14C]methylglucose uptake in isolated villus tip enterocytes was determined. Expression of mRNA for the PGE2 receptor subtypes 1–4 was assayed in enterocytes by reverse transcriptase polymerase chain reaction (RT-PCR).RESULTSIn the perfused small intestine, PGE2 acutely increased absorption of glucose and galactose, but not fructose (which is not a substrate for SGLT1); in isolated enterocytes it stimulated 3-O-[14C]methylglucose uptake. The 3-O-[14C]methylglucose uptake could be inhibited by the cAMP antagonist RpcAMPS and the specific inhibitor of SGLT1, phlorizin. High levels of EP2R mRNA and EP4R mRNA were detected in villus tip enterocytes.CONCLUSIONPGE2acutely increased glucose and galactose absorption by the small intestine via the SGLT1, with cAMP serving as the second messenger. PGE2 acted directly on the enterocytes, as the stimulation was still observed in isolated enterocytes and RT-PCR detected mRNA for the cAMP-increasing PGE2 receptors EP2R and EP4R.