Basolateral outward rectifier chloride channel in isolated crypts of mousecolon

Single channel patch-clamp techniques were used to demonstrate the presence of outwardly rectifying chloride channels in the basolateral membrane of c rypt cells from mouse distal colon. These channels were rarely observed in the cell-attached mode and, in the inside-out configuration, only became ac tive after a delay and depolarizing voltage steps. Single channel conductan ce was 23.4 pS between -100 and -40 mV and increased to 90.2 pS between 40 and 100 mV. The channel permeability sequence for anions was: I- > SCN- > B r- > Cl- > NO3- > F- >> SO42- approximate to gluconate. In inside-out patch es, the channel open probability was voltage dependent but insensitive to i ntracellular Ca2+ concentration. In cell-attached mode, forskolin, histamin e, carbachol, A-23187, and activators of protein kinase C all failed to act ivate the channel, and activity could not be evoked in inside-out patches b y exposure to the purified catalytic subunit of cAMP-dependent protein kina se A. The channel was inhibited by 5-nitro-2-(3-phenylpropylamino)benzoate, 9-anthracenecarboxylic acid, and DIDS. Stimulation of G proteins with guan osine 5'-O-(3-thiotriphosphate) decreased the channel open probability and conductance, whereas subsequent addition of guanosine 5'-O-(2-thiodiphospha te) reactivated the channel.