Absorption of TEA+ by intestine of the American lobster, Homarus americanus

Abstract

A number of organic cation metabolites are actively secreted by both vertebrate and invertebrate renal organs. This process involves the occurrence of a basolateral facilitated diffusion, electrogenic, member of the OCT transporter family coupled with a brush border antiporter shared by protons and organic cations which transfers the organic metabolite out of the cell by secondary active transport. This investigation examined the potential extra-renal role of the lobster intestine in the regulation of organic metabolites. Isolated intestines were immersed in, and perfused by, a physiological saline with a salt composition and pH matching the hemolymph. Radiolabelled 14C-TEA+ was either added to the serosal bath (for S to M flux measurements) or to the perfusate (for M to S flux measurements). Transmural 14C-TEA+ fluxes in both directions for the anterior and posterior intestinal segments were separately measured at [TEA] of 0.1, 0.5, 1.0, and 2.0 mM. Over this concentration range, both M to S and S to M fluxes followed Michaelis-Menten kinetics and saturable net absorptive fluxes were observed in both intestinal regions. Anterior intestine illustrated a 5-fold greater net absorptive flux than the posterior intestine. Net fluxes observed for the 1.0 mM 14C-TEA+ concentration are 7.24 nmol/cm2*min for the anterior intestine and 1.58 nmol/cm2*min for the posterior intestine. These results suggest that lobster intestine is an organic cation absorptive structure, contrasting with the secretory nature of the urinary bladder in this animal and of the vertebrate nephron for this group of metabolites. Supported by NSF grant IBN04-21986.