Isolation of an osmoreceptor (TRPV4) from the avian lower gastrointestinal tract

Abstract

Avian osmoregulation differs from that of mammals in that not only do the kidneys regulate water and electrolyte levels but the lower gastrointestinal tract does as well. From the kidney, urine is conveyed to the cloaca where a reverse peristalsis of the GI tract brings the urine in contact with epithelial tissues of the colon where its composition can be modified. Brummermann and Braun (AJP, 268, 1995) demonstrated that this reverse peristalsis is not centrally regulated but rather locally regulated in the lower gastrointestinal tract. We suggest that the sensor of luminal fluid osmolarity is a member of the vanilloid‐receptor subfamily of transient receptor potential channels (TRPV4) a moderately selective Ca2+ channel. In the present study, tissues from the kidney, cloaca, and colon, were harvested from mourning dove (Zenaida macroura) and homogenized for analysis. Using Western Blotting and Immunohistochemistry, TRPV4 was visualized as the reaction product of DAB as well as a secondary antibody labeled with a fluorescent tag. To show the specific binding of the primary antibody, a blocking peptide was used to disrupt the above reactions. The results of immunohistochemistry show that TRPV4 is localized in the muscularis mucosa of the urodeum and similarly in the muscularis mucosa of the colon. In the avian kidney, TRPV4 appears to be localized in the ascending limbs of Henle similar to that of the mammalian kidney.