Bicarbonate secretion plays a role in chloride and water absorption of the European flounder intestine.

Experiments performed on isolated intestinal segments from the marine teleost fish, the European flounder (Platichthys flesus), revealed that the intestinal epithelium is capable of secondary active HCO3– secretion in the order of 0.2–0.3 µmol·cm–2·h–1 against an apparent electrochemical gradient. The HCO3– secretion occurs via anion exchange, is dependent on mucosal Cl–, results in very high mucosal HCO3– concentrations, and contributes significantly to Cl– and fluid absorption. This present study was conducted under in vivo-like conditions, with mucosal saline resembling intestinal fluids in vivo. These conditions result in a transepithelial potential of –16.2 mV (serosal side negative), which is very different from the –2.2 mV observed under symmetrical conditions. Under these conditions, we found a significant part of the HCO3– secretion is fueled by endogenous epithelial CO2 hydration mediated by carbonic anhydrase because acetazolamide (10–4 M) was found to inhibit HCO3– secretion and removal of serosal CO2 was found not to influence HCO3– secretion. Reversal of the epithelial electrochemical gradient for Cl– (removal of serosal Cl–) and elevation of serosal HCO3– resulted in enhanced HCO3– secretion and enhanced Cl– and fluid absorption. Cl– absorption via an anion exchange system appears to partly drive fluid absorption across the intestine in the absence of net Na+ absorption

Intestinal iron uptake in the European flounder (Platichthys flesus)

Iron is an essential element because it is a key constituent of the metalloproteins involved in cellular respiration and oxygen transport. There is no known regulated excretory mechanism for iron, and homeostasis is tightly controlled via its uptake from the diet. This study assessed in vivo intestinal iron uptake and in vitro iron absorption in a marine teleost, the European flounder Platichthys flesus. Ferric iron, in the form 59FeCl3, was reduced to Fe2+ by ascorbate, and the bioavailability of Fe3+ and Fe2+ were compared. In vivo Fe2+ uptake was significantly greater than Fe3+ uptake and was reduced by the iron chelator desferrioxamine. Fe2+ was also more bioavailable than Fe3+ in in vitro studies that assessed the temporal pattern and concentration-dependency of iron absorption. The posterior region, when compared with the anterior and mid regions of the intestine, was the preferential site for Fe2+ uptake in vivo. In vitro iron absorption was upregulated in the posterior intestine in response to prior haemoglobin depletion of the fish, and the transport showed a Q10 value of 1.94. Iron absorption in the other segments of the intestine did not correlate with haematocrit, and Q10 values were lower. Manipulation of the luminal pH had no effect on in vitro iron absorption. The present study demonstrates that a marine teleost absorbs Fe2+ preferentially in the posterior intestine. This occurs in spite of extremely high luminal bicarbonate concentrations recorded in vivo, which may be expected to reduce the bioavailability of divalent cations as a result of the precipitation as carbonates (e.g. FeCO3)

Screening and the construction of scepticism: the case of Chlamydia

Screening for disease is an integral component of UK preventative health policy, and there are proposals to introduce a screening programme for the sexually transmitted infectionChlamydia trachomatis. In recent years, however, debates over screening have been characterized by increasing scepticism about the individual benefits of participating in such initiatives. This article explores factors that may contribute to this scepticism, in the context of a study that investigated the experience of women who had been diagnosed with chlamydia. We employ Bury's concept of 'risk to meanings' to understand better the social process of the development of uncertainty in relation to a positive diagnosis. Three themes related to uncertainty and the 'risk to meaning' are explored here - the threat to self-image, disclosing diagnosis and anxiety about future health status. The implications for the proposed UK chlamydia screening programme are discussed, and the article suggests that the development and construction of scepticism occurs in the space between expectations stimulated by public health discourses of screening and the lived experience of individuals