β-Adrenergic activation of electrogenic K+ and Cl- secretion in guinea pig distal colonic epithelium proceeds via separate cAMP signaling pathways

Halm ST, Zhang J, Halm DR. beta-Adrenergic activation of electrogenic K+ and Cl- secretion in guinea pig distal colonic epithelium proceeds via separate cAMP signaling pathways. Am J Physiol Gastrointest Liver Physiol 299: G81-G95, 2010. First published April 22, 2010; doi:10.1152/ajpgi.00035.2010.-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 (I-epi(sc)). Inhibition of transmembrane adenylyl cyclases (tmACs) reduced peak I-epi(sc) and cAMP to near zero without decreasing sustained I-epi(sc), consistent with cAMP from tmAC signaling for only Cl- secretion. Inhibition of soluble adenylyl cyclase (sAC) reduced sustained I-epi(sc) and cAMP to near zero without decreasing peak I-epi(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 I-epi(sc) but not sustained I-epi(sc), consistent with these PDEs as part of the beta(2)-AdrR signaling domain. PYY suppressed peak I-epi(sc) in a pertussis toxin (PTx)-sensitive manner, supporting G alpha(i)-dependent inhibition of tmACs producing cAMP for Cl- secretion. Since PYY or PTx did not alter sustained I-epi(sc), signaling for K+ secretion occurred via a G alpha(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 I-epi(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.