Fig 1.
Isc responses to apical and basolateral bumetanide in early and late distal colon of rats.
Measurements were made in normal Ringer solution. Note that while apical bumetanide (100 μM) had no effect on either colonic segment, basolateral bumetanide (100 μM) induced two opposite Isc responses: inhibitory in early but stimulatory in late distal colon. ap, apical; bl, basolateral. ** P<0.01 vs. absence of bumetanide using paired t test. N = 10.
Table 1.
Basal bioelectric parameters in rat early and late distal colon.
Fig 2.
Isc responses to basolateral bumetanide in the presence of amiloride and barium.
Isc was measured in normal Ringer solution. Note that amiloride (10 μM, apical) significantly decreased and barium (5 mM, apical) significantly increased Isc in late distal colon. However, these treatments did not alter the subsequent Isc responses to bumetanide (100 μM, basolateral) in either colonic segment. Subsequent addition of forskolin (500 nM, basolateral) caused Isc stimulation in both segments (see text). * P<0.05 and ** P<0.01 vs. prior treatment by paired t test. N = 10.
Table 2.
Effects of amiloride and benzamil on ΔIscAmiloride and ΔIscBumetanide in rat early and late distal colon*.
Fig 3.
Effects of ion substitution on changes in Isc responses to basolateral bumetanide (100 μM) in early vs. late distal colon.
Note the two opposing ΔIscBumetanide: negative or inhibitory in early distal colon and positive or stimulatory in late distal colon. While Na+ substitution caused no significant change in the Isc response in either colonic segment, removal of Cl- from media abolished the Isc responses in both segments. ** P<0.01 vs. control. N = 8–12.
Fig 4.
Effects of Cl- channel inhibitors on Isc responses to basolateral bumetanide in early and late distal colon of rats.
Measurements were made in normal Ringer solution. Note that pretreatment with NPPB (100 μM, apical) and glibenclamide (300 μM, apical) significantly attenuated Isc responses to bumetanide (100 μM, basolateral) and forskolin (500 nM, basolateral), but not to amiloride (10 μM, apical) or carbachol (CCH, 100 μM, basolateral). **P<0.05 vs. (-) NPPB/Glibenclamide. N = 5.
Fig 5.
Transepithelial conductance (GT) responses to bumetanide (100 μM, basolateral) and forskolin (500 nM, basolateral) in early and late distal colon of rats.
The experiments were performed in normal Ringer solution. ** P<0.01 vs. prior drug treatment. N = 10.
Fig 6.
Differential expression of gene transcripts in late distal colon of rats relative to early distal colon.
Positive values indicate more abundant transcripts of indexed gene in late than in early distal colon whereas negative values indicate less abundant transcripts of indexed gene in late than in early distal colon. * P<0.05 vs. early distal colon.
Table 3.
Differential expression of gene transcripts in rat distal colon.
Fig 7.
Differential expression of KCC1 protein in late distal colon of rats relative to early distal colon.
Upper panel, Western blots of KCC1; Middle panel, Ponceau S staining; Lower panel, The Western blots were quantified and normalized to ponceau S staining. The y-axis represents relative values (changes in fold) with respect to the values of early distal colon. * P<0.05 vs. early distal colon. N = 5.
Fig 8.
Effects of dietary Cl- depletion and repletion on Isc responses to basolateral bumetanide in early and late distal colon.
Note that dietary Cl- depletion enhanced whereas dietary Cl- repletion reduced the positive Isc induced by basolateral bumetanide (100 μM) in late distal colon but had no effect on the induced negative Isc in early distal colon. * P<0.05 and ** P<0.01 vs. normal Cl- diet. N = 6–10.
Table 4.
IscAmiloride responses to low and high salt diet treatments in rat distal colon.
Fig 9.
Transport model for electrogenic Cl- absorption in surface cell of late distal colonic epithelium.
Cl- enters via a Cl- channel conductance and egresses through a bumetanide-sensitive K+-Cl- cotransporter. K+ is recycled uphill into the cell by Na+,K+-ATPase (NKA), while the latter pumps Na+ that enters via ENaC against electrochemical gradient out of the cell. Thus, transepithelial Na+ and Cl- absorption are both an active process and operate in parallel.