Adrenergic activation of electrogenic K + secretion in guinea pig distal colonic epithelium: involvement of β1- and β2-adrenergic receptors
Adrenergic stimulation of electrogenic K + secretion in isolated mucosa from guinea pig distal colon required activation of two β-adrenergic receptor subtypes (β-AdrR). Addition of epinephrine (epi) or norepinephrine (norepi) to the bathing solution of mucosae in Ussing chambers increased short-circ...
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Published in | American journal of physiology: Gastrointestinal and liver physiology Vol. 297; no. 2; pp. G269 - G277 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
American Physiological Society
01.08.2009
|
Subjects | |
Online Access | Get full text |
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Summary: | Adrenergic stimulation of electrogenic K
+
secretion in isolated mucosa from guinea pig distal colon required activation of two β-adrenergic receptor subtypes (β-AdrR). Addition of epinephrine (epi) or norepinephrine (norepi) to the bathing solution of mucosae in Ussing chambers increased short-circuit current ( I
sc
) and transepithelial conductance ( G
t
), consistent with this cation secretion. A β-adrenergic classification was supported by propranolol antagonism of this secretory response and the lack of effect by the α-AdrR antagonists BE2254 (α1-AdrR) and yohimbine (α2-AdrR). Subtype-selective antagonists CGP20712A (β1-AdrR), ICI-118551 (β2-AdrR), and SR59320A (β3-AdrR) were relatively ineffective at inhibiting the epi-stimulated I
sc
response. In combination, CGP20712A and ICI-118551 inhibited the response, which supported a synergistic action by β1-AdrR and β2-AdrR. Expression of mRNA for both β1-AdrR and β2-AdrR was indicated by RT-PCR of RNA from colonic epithelial cells. Protein expression was indicated by immunoblot showing bands at molecular weights consistent with monomers and oligomers. Immunoreactivity (ir) for β1-AdrR and β2-AdrR was prominent in basolateral membranes of columnar epithelial cells in the crypts of Lieberkühn as well as intercrypt surface epithelium. Cells in the pericryptal sheath also had β1-AdrR
ir
but did not have discernable β2-AdrR
ir
. The adrenergic sensitivity of K
+
secretion measured by I
sc
and G
t
was relatively low as indicated by EC
50
s of 41 ± 7 nM for epi and 50 ± 14 nM for norepi. Adrenergic activation of electrogenic K
+
secretion required the involvement of both β1-AdrR and β2-AdrR, occurring with an agonist sensitivity reduced compared with reported values for either receptor subtype. |
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Bibliography: | Address for reprint requests and other correspondence: D. Halm, Dept. of Neuroscience, Cell Biology, and Physiology, Wright State Univ. Boonshoft School of Med., 3640 Colonel Glenn Hwy., Dayton, OH 45435 (e-mail: dan.halm@wright.edu) |
ISSN: | 0193-1857 1522-1547 |
DOI: | 10.1152/ajpgi.00076.2009 |