-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. -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 (Isc) depended on 2-adrenergic receptors ( 2-AdrR), and sustained Isc relies on a 1-AdrR/ 2-AdrR complex. Epinephrine (epi) increased cAMP content with a biphasic time course similar to changes in epi-activated Isc (Isc). Inhibition of transmembrane adenylyl cyclases (tmACs) reduced peak Isc and cAMP to near zero without decreasing sustained Isc, consistent with cAMP from tmAC signaling for only Cl secretion. Inhibition of soluble adenylyl cyclase (sAC) reduced sustained Isc and cAMP to near zero without decreasing peak Isc 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 Isc but not sustained Isc, consistent with these PDEs as part of the 2-AdrR signaling domain. PYY suppressed peak Isc in a pertussis toxin (PTx)-sensitive manner, supporting G i-dependent inhibition of tmACs producing cAMP for Cl secretion. Since PYY or PTx did not alter sustained Isc, signaling for K secretion occurred via a G 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 Isc, but the cAMP-dependent guanine nucleotide exchange factor, Epac, may contribute. Thus -adrenergic activation of electrogenic Cl and K secretion, respectively, required tmACand sACdependent signaling pathways.