Cyclic-gmp stimulates sodium and chloride currents in rat tracheal
airway epithelia.
Schwiebert, Erik M., Elizabeth D. Potter, Tae-Ho Hwang, Jae Suk Woo,
Changlin Ding, Weiping Qiu, William B. Guggino, Michael A. Levine,
and Sandra E. Guggino.
Divisions of Gastroenterology and Endocrinology, Department of
Medicine; and Departments of Neuroscience and Physiology, Johns
Hopkins School of Medicine, 929 Ross Building, 720 Rutland Ave,
Baltimore, Md. 21205
APStracts 3:0303C, 1996.
To test the hypothesis that cGMP regulates ion transport in airway
epithelial cells, we measured short circuit current (ISC) and 22Na+
fluxes in primary cultured rat tracheal epithelial cells. In Cl-
containing Ringer's, ISC was increased by approximately 17[mu]A/cm2
after application of 1mM 8-Br-cGMP, whereas, in Cl--free solutions,
the sodium-mediated component was approximately 5[mu]A/cm2,
suggesting a cGMP stimulation of Cl- secretory current (ICl) and a
smaller sodium absorptive current ( INa). Inward and net mucosal to
serosal 22Na+ flux was doubled in the presence of 2 mM 8-Br-cGMP. To
determine whether nucleotide-gated channels play a role in this
transepithelial Na+ absorption, blockers of nucleotide-gated cation
channels were used to inhibit ISC. The cGMP-stimulated sodium
-mediated ISC was blocked by as little as 500 nM dichlorobenzamil or
50 [mu]M l-cis-diltiazem, which are known blockers for cyclic
nucleotide-gated cation channels. These agents also blocked the basal
(non-cGMP-stimulated) current when measured in the presence of 10
[mu]M amiloride which blocks current through 5 pS amiloride-sensitive
sodium channels. To document whether the distribution of nucleotide
-gated nonselective cation channels was consistent with a role in
airway epithelial transport, in situ hybridization was performed. In
situ hybridization of mRNA encoding for nucleotide-gated cation
channels was found in epithelial cell layers of rat trachea, bronchi,
bronchioles, and alveolar cells but not in smooth muscle layers or
tracheal cartilage. Reverse transcriptase polymerase chain reaction
(RT-PCR), restriction enzyme analysis, and sequencing of the cDNA
transcribed from mRNA of whole lung and tracheal epithelial cells,
indicates that a channel highly homologous to the retinal nucleotide
-gated non-selective cation channel (CNG1) is present. Thus, these
data along with evidence supporting the existence of signal
transduction pathways elevating intracellular levels of cGMP,
indicate that cGMP regulates transepithelial ion transport in lung
epithelial tissues.
Received 20 November 1995; accepted in final form 17 September
1996.
APS Manuscript Number C698-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996