AJP - Gastrointestinal and Liver Physiology, Vol 250, Issue 4 475-G483, Copyright © 1986 by American Physiological Society
Active potassium secretion by rabbit proximal colon
S. K. Sullivan and P. L. Smith
Fluxes of K from mucosa to serosa or serosa to mucosa have been examined in
stripped preparations of rabbit proximal and distal colon in vitro under
short-circuit conditions in Ussing chambers. Results from these studies
demonstrate that steady-state radioisotopic fluxes of K are achieved after
90 min and remain constant for at least 2 h. Determination of the K
concentration dependence of the serosal-to-mucosal K flux revealed that
this flux contains both saturable and nonsaturable components. Addition of
ouabain (0.1 mM) abolished the saturable component of the
serosal-to-mucosal K flux. The mucosal-to-serosal K flux is a linear
function of K concentration between 1 and 20 mM under basal conditions. In
paired tissues, serosal-to-mucosal K flux is always greater than
mucosal-to-serosal flux under basal conditions resulting in net K
secretion. However, addition of barium (2 mM) to the mucosal or serosal
bathing solution had no significant effect on either unidirectional or net
K fluxes. In addition, mucosal bumetanide (0.1 mM) or removal of Cl from
both bathing solutions had no significant effect on unidirectional or net K
fluxes. In rabbit distal colon, Cl removal from the bathing solutions
significantly reduced serosal-to-mucosal K flux, resulting in net K
absorption. These results indicate that rabbit proximal colon like rabbit
distal colon actively secretes K. However, unlike distal colon the proximal
colon does not possess an active K uptake mechanism at the apical cell
membrane.(ABSTRACT TRUNCATED AT 250 WORDS)
