SODIUM-DEPENDENT TRANSEPITHELIAL WATER FLUXES OF THE VOCAL FOLD
Kimberly Fisher1
Danielle Lodewyck1
Alvin Telser2
John Phillips3
Donovan Yeates3
1Northwestern University, 2Northwestern Medical School, 3University of Illinois Chicago
In a search for mechanisms that govern vocal fold hydration and phonation, we posited that vocal fold epithelium generates bidirectional water fluxes which are regulated by activity of the Na+,K+-ATPase and require presence of the amiloride-sensitive epithelial sodium channel (ENaC). To confirm the presence of Na+,K+-ATPase and ENaC in canine and ovine vocal folds, we performed immunohistochemistry visualized by light and electron microscopy. We next assayed electrophysiology and water fluxes of viable vocal fold mucosae before and after administration of an irreversible Na+,K+-ATPase inhibitor (acetylstrophanthidin) and reversible ENaC blocker (amiloride). Immunohistochemistry demonstrated a non-uniform distribution of the a-subunit Na+,K+-ATPase, as well as the a- and b -subunit proteins of ENaC across the stratified epithelium. Luminal cells possessed high labeling density for ENaC and intense staining for Na+,K+-ATPase. Lumen negative potential differences (PD canine= 8.1+2.8 mV, PD ovine= 9.3+1.3 mV) and short circuit currents (Isc canine = 41 + 10 mA/cm2 , Isc ovine = 31 + 4 mA/cm2) were reduced slowly (time constant = 1400 sec) by luminal administration of 75 mM acetylstrophanthidin (p<0.05) and rapidly (time constant = 30 sec) by luminal amiloride (p<0.05). Baseline ovine transepithelial water fluxes (both secretion and absorption ≈5 ml/min/cm2) were decreased by administration of luminal acetylstrophanthidin (p<0.05). Luminal amiloride reduced water absorption (p<0.05), but increased secretion. Results support our model wherein a sodium-dependent, water-absorptive pathway is associated with a luminally-directed couterion and water flux. The Na+,K+-ATPase, and ion/water fluxes derived from its activity, provide an adaptive mechanism to regulate vocal fold hydration. The distribution of Na+,K+-ATPase and ENaC in the vocal fold further suggests specialization of cell layers within a stratified epithelial organ, and may allow this epithelium to fine tune the rheology, volume, shape and/or sensory function of the vocal fold cover. Such a system appears necessary in the osmotically and biomechanically challenging environment of the vocal fold. Topical, pharmacologic treatments to manipulate epithelial water/ion flux may lead to new treatments for voice and laryngeal disorders.
Work was conducted under approved protocols at Northwestern University and University of Illinois Chicago. Research was supported by the NIDCD K08DC00168; Northwestern University Department of Communication Sciences and Disorders; and Department of Medicine, University of Illinois Chicago. The authors acknowledge technical assistance of Bert Menco and Sharon Lang. Part of the work was published elsewhere (Fisher, et al.,2001, J Appl Physiol 91).
Preferred format: Oral presentation
Audiovisual: Computer powerpoint presentation
SODIUM-DEPENDENT TRANSEPITHELIAL WATER FLUXES OF THE VOCAL FOLD
Kimberly Fisher
Danielle Lodewyck
Alvin Telser
Donovan Yeates
Correspondence should be directed to the first author:
Kimberly V. Fisher
Northwestern University
Department of Communication Sciences and Disorders
2299 N. Campus Drive
Evanston, IL 60208
phone 847-491-2433
fax 847-4672776
Danielle Lodewyck
Northwestern University
Department of Communication Sciences and Disorders
2299 N. Campus Drive
Evanston, IL 60208
phone 847-491-2433
fax 847-467-2776
Alvin G. Telser
Northwestern Medical School
Department of Cell and Molecular Biology
phone 312-503-8276
fax 312-503-7912
Donovan B Yeates
University of Illinois Chicago
Pulmonary Engineering and Biophysics
phone 312-996-6464
fax 312-996-1286