Size and charge selectivity of the Intestinal paracellular absorption of hydrosoluble compounds in house sparrows (Passer domesticus).

JUAN GABRIEL CHEDIACK; FASULO, V.; CAVIEDES-VIDAL, E.; KARASOV, W.

Riberao Preto

Congreso; XXI Congresso da Associação Latino Americana de Ciências Fisiológicas; 2003

Sociedade Brasileira de Fisiologia y Associação Latino Americana de Ciências Fisiológicas

Size and charge selectivity OF THE intestinal paracellular absorption of hydrosoluble compounds in house sparrows (Passer domesticus). Chediack, Juan1, Fasulo, Verónica1, Karasov, William2 and Caviedes-Vidal, Enrique1. 1Departamento Bioquímica y Ciencias Biológicas. Universidad Nacional de San Luis. Argentina. 2Department of Wildlife Ecology. University of Wisconsin, Madison. USA. E-mail: jchedi@unsl.edu.ar We are characterizing the apparent paracellular permeability of the small intestine in intact birds. We previously found that absorption of L-glucose (stereoisomer that does not interact with SGLT1 transporter) and other non-electrolytes probes (D-mannitol and L-arabinose) was substantial (between 60 to 80%). In this study we extend the scope of our previous findings in two experiments. First, using other non actively transported probes (L-arabinose MW 150.1, L-rhamnose MW 164.2, perseitol MW 212.2 and lactulose MW=342.3) with increasing molecular weight (MW). Second, using two indigestible dipeptides (synthesized using D-aminoacids) that were highly hydrophilic and similar in MW: Ser-Lys (positive at pH 7.4, MW 233) and Ser-Asp (negative at pH 7.4 MW 220). Objectives: 1) to test for size dependency of the paracellular absorption pathway using a series of nonelectrolyte hydrosoluble carbohydrates that differ in molecular dimensions. 2) to test the electroaffinity of paracellular pathway with small model peptides, and 3) to investigate how much is enhanced the paracellular transport in the movement of substances by charge effect. Methods: To this purpose we use a whole house sparrow as a model. Isosmotic solutions with probes were gavaged into the stomach in nonanesthetized House sparrows (Passer domesticus), and injected in the pectoralis with a syringe in different trials. Using a pharmacokinetic approach involving a serial blood collection the bioavailability (F) was calculated with a classical equation as F=[AUC by gavage)]/[AUC by injection] (AUC = area under the curve of plasma probe concentration vs. time). Results: Bioavailability declined linearly with probe size a total of 75% from the smallest to the largest probe (0.61 + 0.09 to 0.15 + 0.05 P<0.001) and was about half for the negatively charged dipeptide that of the positively charged dipeptide (0.17+ 0.03 vs 0.30 + 0.05, respectively P< 0.03). Conclusions: These findings suggest that passive paracellular absorption across the small intestine varies inversely with the size of the probes and positively-charged solutes has preference to be absorbed. Our research defines the selectivity of the pathway against large and negatively charged molecules. It can lead to improved prediction of hydrosoluble toxin bioavailability and design of new pesticides. Supported by FONCYT (01-03101), CyT-UNSL (9502) to EC-V and NSF (IBN-0216709) to WHK.