EVIDENCE OF MENTHOL-MEDIATED AMMONIUM TRANSPORT VIA TRANSIENT RECEPTOR POTENTIAL (TRPV3 AND TRPM6) CHANNELS ACROSS ISOLATED RUMEN AND OMASUM EPITHELIA OF BUFFALO (BUBALUS BUBALIS)

Abstract

Fermentative protein degradation to ammonia and excretion of nitrogenous compounds from ruminants is a global environmental concern. Exploration of ammonia uptake mechanisms in the fore-stomach of ruminants is one of the approaches to tackle this issue. In cattle, channel-mediated ammonium uptake in the rumen is well established and occurs via transient receptor potential (TRP) channels with a sensitivity to essential oils. However, the expression, sensitivity, and role of these channels in the fore-stomach of buffaloes (Bubalus bubalis) remains to be ascertained. This study investigated the functional expression of TRP channels in indigenous buffalo's rumen and omasal epithelia and their involvement in menthol-mediated ammonia transport. Viable segments of rumen and omasum epithelia were collected immediately from slaughtered adult indigenous buffalo (N=8) for molecular expression of TRP channels. The isolated epithelia were mounted on Ussing chambers with mucosal buffer solutions containing NH₄Cl (0mM, 10mM, and 40mM and osmolarity 300, 350, or 400 mosmol·l^-1) with or without menthol. Results showed that TRPV3 and TRPM6 were expressed in both rumen and omasum epithelia; however, the expression was significantly lower in omasum. In vitro experiments with isolated ruminal and omasal epithelia exposed to varied mucosal ammonium buffer revealed a menthol-sensitive short-circuit current (rumen > omasum) and acidification of serosal buffer. An increase in mucosal osmotic pressure increased transepithelial tissue conductance, which was not influenced by mucosal menthol. This study suggests that TRP channels are expressed in the rumen and omasum epithelia of buffalo and are involved in menthol-sensitive ammonium transport. Further research on these channels could help mitigate ammonia release from livestock.