title: beta-Adrenergic activation of electrogenic K+ and Cl- secretion in guinea pig distal colonic epithelium proceeds via separate cAMP signaling pathways.
abstract: Adrenergic stimulation of isolated guinea pig distal colonic mucosa produced transient Cl(-) and sustained K(+) secretion. Transient short-circuit current (I(sc)) depended on beta(2)-adrenergic receptors (beta(2)-AdrR), and sustained I(sc) relies on a beta(1)-AdrR/beta(2)-AdrR complex. Epinephrine (epi) increased cAMP content with a biphasic time course similar to changes in epi-activated I(sc) ((epi)I(sc)). Inhibition of transmembrane adenylyl cyclases (tmACs) reduced peak (epi)I(sc) and cAMP to near zero without decreasing sustained (epi)I(sc), consistent with cAMP from tmAC signaling for only Cl(-) secretion. Inhibition of soluble adenylyl cyclase (sAC) reduced sustained (epi)I(sc) and cAMP to near zero without decreasing peak (epi)I(sc) or cAMP, consistent with cAMP from sAC signaling for K(+) secretion. Sensitivity to phosphodiesterase (PDE) inhibitors and peptide YY (PYY) stimulation further supported separate signaling for the two components. PDE3 or PDE4 inhibitors enhanced peak (epi)I(sc) but not sustained (epi)I(sc), consistent with these PDEs as part of the beta(2)-AdrR signaling domain. PYY suppressed peak (epi)I(sc) in a pertussis toxin (PTx)-sensitive manner, supporting Galpha(i)-dependent inhibition of tmACs producing cAMP for Cl(-) secretion. Since PYY or PTx did not alter sustained (epi)I(sc), signaling for K(+) secretion occurred via a Galpha(i)-independent mechanism. Presence of multiple sAC variants in colonic epithelial cells was supported by domain-specific antibodies. Responses to specific activators and inhibitors suggested that protein kinase A was not involved in activating peak or sustained components of (epi)I(sc), but the cAMP-dependent guanine nucleotide exchange factor, Epac, may contribute. Thus beta-adrenergic activation of electrogenic Cl(-) and K(+) secretion, respectively, required tmAC- and sAC-dependent signaling pathways.
authors.affiliation: Department of Neuroscience, Cell Biology and Physiology, Wright State University Boonshoft School of Medicine, 3640 Colonel Glenn Hwy., Dayton, OH 45435, USA.
authors.forename: Susan T
authors.initials: ST
authors.lastname: Halm
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Dan R
authors.initials: DR
authors.lastname: Halm
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D020536:Enzyme Activators / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007419:Intestinal Secretions / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials; D019894:Peptide YY / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D018342:Receptors, Adrenergic, beta-1 / Q000378:metabolism*; D018343:Receptors, Adrenergic, beta-2 / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013997:Time Factors
chemical_list: D000318:Adrenergic beta-Agonists; D000319:Adrenergic beta-Antagonists; D001639:Bicarbonates; D002712:Chlorides; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D018342:Receptors, Adrenergic, beta-1; D018343:Receptors, Adrenergic, beta-2; D019894:Peptide YY; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D000262:Adenylyl Cyclases; D011188:Potassium