β-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.

Role of the BK channel (KCa1.1) during activation of electrogenic K+ secretion in guinea pig distal colon

“…Treatment with the ␤2-adrenergic receptor antagonist ICI-118551 suppressed the Cl Ϫ secretory transient (25,87) which revealed the full K ϩ secretory time course. IbTx (300 nM) added during epinephrine stimulation produced greater inhibition of epi I sc with paxilline (1.0 M) present, and approached the fractional inhibition produced by 10 M paxilline alone ( Fig.…”

Dual activation of CFTR and CLCN2 by lubiprostone in murine nasal epithelia

“…CFTR is known to be activated through a cAMP-PKA-dependent signaling pathway, and the importance of the EP4 receptor in increasing intracellular cAMP in response to lubiprostone in sheep airways, leading to CFTR activation, has been demonstrated (13). Concurrently, PKAindependent alternative pathways to chloride secretion are well documented, including the Epac pathway, which can activate protein kinase B (PKB) (17)(18). Lubiprostone may activate CLCN2 through a similar PKA-independent pathway; recent data suggests CLCN2 conductance is upregulated by a serum and glucocorticoid inducible kinase, SGK1, and PKB (31).…”

Stress at the intestinal surface: catecholamines and mucosa–bacteria interactions

“…These effects are generally mediated by alpha-adrenergic receptors located on enteric neurons projecting to the epithelium or the epithelial cells per se (Field and McColl 1973;Chang et al 1983;Dharmsathaphorn et al 1984;Fondacaro et al 1988;Hildebrand et al 1993). In the colon, however, these catecholamines can act on alpha-or beta-adrenergic receptors to evoke potassium, bicarbonate or chloride secretion depending upon mammalian species and colonic segment (Sullivan and Smith 1986;Sellin and De Soignie 1987;Hörger et al 1998;Lam et al 2003;Zhang et al 2008;Halm et al 2010).…”