β‐adrenergic stimulation of K secretion in guinea pig distal colon through activation of both Cl and K conductances

Abstract

K secretion was measured as whole‐cell currents in isolated colonic crypts as well as short‐circuit current (Isc) and transepithelial conductance (Gt) in guinea pig distal colonic mucosa. Colonic crypts isolated from basement membrane were sealed with patch pipets and standard whole cell obtained. Currents recorded at K reversal potential were defined as predominantly Cl currents (ICl) and those at Cl reversal potential were K currents (IK). Epinephrine (epi) [10μM] stimulation resulted in a 1.4‐fold increase in IK that was maximal within 2min; a 1.8‐fold increase in ICl occurred that reached maximal levels within 5min. Epi stimulated negative Isc consistent with K secretion that was near maximum by 10min; Gt increased in parallel with Isc activation. K secretory Isc was largely inhibited by addition of glibenclamide (glib) to either mucosal or serosal bathing solution with an EC50 of ~200μM. Addition of glib to both sides increased sensitivity, EC50 ~40μM. Glib [100μM] eliminated epi activated IK and ICl in crypts within 2min; ICl decreased further over the succeeding 10min indicating that basal ICl also was partially glib‐sensitive. Mucosal expression was detected by RT‐PCR for glib‐sensitive K channel proteins Kir6.1 and Kir6.2 and accessory subunits SUR1 and SUR2. Thus, K secretion likely involves glib‐sensitive K and Cl channels present in apical and basolateral membranes of colonic crypts. [NIH DK65845]