Am. J. Respir. Cell Mol. Biol.,
Volume 22, Number 3, March, 2000 373-379
Effects of Methacholine and Uridine 5'-Triphosphate on Tracheal Mucus
Rheology in Mice
Eiichi
Sudo,
Martin M.
Lee,
William A.
Boyd,
and
Malcolm
King
Pulmonary Research Group, University of Alberta, Edmonton, Canada
We compared the action of methacholine (MCh) and uridine 5'-triphosphate (UTP) with and without pretreatment with the chloride channel blocker 4,4'-diisothiocyano-2,2'-stilbenedisulfonate (DIDS) on the
transepithelial potential difference (PD), the mucus collection rate (MCR), and tracheal mucus rheology
using anesthetized C57BL/6 mice. The cystic fibrosis transmembrane conductance regulator (CFTR)
blocker 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB) was also used as a pretreatment for MCh. After
collecting baseline mucus for 1.5 h, mucus secretion was stimulated by instilling 5 µl of 10
2 M MCh
or UTP around the upper trachea. There was a significant increase in PD after MCh or UTP stimulation
(
21.3 ± 2.0 mV MCh versus 14.1 ± 1.6 mV control; 25.4 ± 2.5 mV UTP versus 19.2 ± 1.9 mV
control). When UTP administration was preceded by DIDS, PD shifted from 15.2 ± 2.9 to 12.0 ± 2.2 mV. When MCh was preceded by DIDS or by NPPB, there was no change in PD. There was a significant decrease in mucus rigidity index, logG*, with MCh (2.54 ± 0.09 versus 2.99 ± 0.14 for control), similar
to that previously reported in other species. With UTP, 14 of 16 mice responded in terms of PD becoming
more negative, and of these, there was a significant difference in logG* after UTP administration (2.29 ± 0.10 versus 2.57 ± 0.10 for control), whereas there was no change in logG* with DIDS administration before UTP. When DIDS administration preceded MCh, there was a diminished but still significant decrease in logG* from control, whereas there was no change in logG* when NPPB was preadministered. The control mucus collection rate was 0.19 ± 0.09 mg/h, whereas after MCh stimulation, it increased to 2.83 ± 0.78 mg/h. No significant difference was measured in the MCR after either UTP or DIDS+UTP stimulation. DIDS+MCh and NPPB+MCh both resulted in significant increases in MCR, but of a much smaller
magnitude than that for MCh alone. We conclude that hypersecretion owing to UTP in C57BL/6 mice is
less vigorous than with MCh, reflecting the limited population of Ca2+-dependent Cl channels stimulated
by UTP P2 receptors. The action of MCh on tracheal mucus secretion in mice appears to involve both
CFTR- and non-CFTR-dependent chloride channels.
