Water-handling epithelia are sensitive to the osmotic environment. In this study, the effects of a hypo-osmotic challenge on carbachol (CCh)-induced fluid secretion was investigated using an ex vivo submandibular gland perfusion technique and intracellular pH and Ca2+ measurements. The osmolality of the perfusion solution was altered to examine the response of the gland to a hypotonic challenge. The flow rate was increased by 34% with a 30% hypotonic solution (225 mOsm), although the Ca2+ response was unchanged. Lowering the external Cl- by 50% abolished this increase in the 30% hypotonic solution. Furthermore, bumetanide, an inhibitor of the Na+-K+-2Cl- co-transporter, completely inhibited the fluid secretion increase caused by the 30% hypotonic solution, and both the total amount of fluid and the flow rate were identical to those of the isotonic solution. This finding was confirmed by measuring Na+-K+-2Cl- co-transporter, bumetanide-dependent NH4+ transport; Na+-K+-2Cl-- transport was up-regulated more than 40% by a 30% hypotonic challenge. Therefore, the increase in CCh-induced fluid secretion in response to hypotonic conditions can be attributed to a large extent to the specific activation of the Na+-K+-2Cl- co-transporter.
- Na+-K+-2Cl- co-transporter
- Saliva secretion
- NH3-NH4+ pre-pulse technique
- Copyright © 2012, American Journal of Physiology - Renal Physiology