ABSTRACT
Intestinal secretory response is altered during colonic development. The aim of this report was to study the developmental changes of the Ca(2+)- and cAMP-induced regulatory pathways with special attention to the direct and indirect effect of secretagogues on the colonic epithelium. We investigated the effect of bethanechol, 5-hydroxytryptamine (5-HT), and histamine on Cl(-) secretion and stimulation of intracellular Ca(2+) ([Ca(2+)](i)) and cAMP in the distal colon of suckling, weanling and adult rats. In the presence of tetrodotoxin, immature colon of suckling and weanling rats displayed higher potency (EC(50)) of 5-HT to stimulate Cl(-) secretion, whereas the potency of histamine was not changed during development. The potency of bethanechol was reduced during weaning and partially restored in adulthood. 5-HT increased cAMP level similarly in both neonatal and adult colonic crypts, but the adults had higher basal level of cAMP than suckling rats. Also the effect of bethanechol on [Ca(2+)](i) was independent of colonic maturation. The results suggest that colonic Cl(-) secretion displays developmental changes of regulation depending on the non-neural secretagogue-signalling pathway and that these developmental changes seem to be localized somewhere outside colonocytes.
Subject(s)
Colon/physiology , Age Factors , Animals , Animals, Suckling , Bethanechol/pharmacology , Calcium/metabolism , Colon/drug effects , Colon/metabolism , Cyclic AMP/metabolism , Dose-Response Relationship, Drug , Electrophysiology , Epithelium/drug effects , Epithelium/physiology , Female , Histamine/pharmacology , Hydroquinones/pharmacology , In Vitro Techniques , Intestinal Mucosa/drug effects , Intestinal Mucosa/metabolism , Male , Rats , Rats, Wistar , Serotonin/pharmacology , Tetrodotoxin/pharmacology , Theophylline/pharmacology , WeaningABSTRACT
The expression patterns of plasma membrane transporters and channels undergo developmental changes during cell differentiation and postnatal development. Until now, little is known about cell membrane conductances during maturation of intestinal crypts even though it is accepted that the crypts undergo dramatic changes during this period of life. Using the whole-cell patch clamp technique, we investigated the developmental changes of potassium conductance (GK) in rat colonic crypts and its heterogeneity along the crypt-surface axis. The resting membrane potential of immature crypts was sensitive to Ba2+ and was higher than in mature crypts. The whole cell conductance during outward currents was higher in immature crypts than in the crypts of adult animals and was reduced by Ba2+ and tetraethylammonium (TEA). With Na+-containing Ringer solution in the bath and K+-containing solution in the pipette, Ba2+- and TEA-sensitive outward currents and conductances were higher in immature than in mature crypts. The TEA-sensitive conductance in immature crypts was distributed heterogenously along the crypt-surface axis with higher values in undifferentiated cells of the crypt base than in differentiated cells of the crypt surface. These data indicate that (1) both colonocyte differentiation and maturation of colonic crypt epithelium are associated with decreasing GK and (2) the axial heterogeneity already exists early in postnatal life when the colonic epithelium undergoes rapid proliferation and growth associated with elongation and bifurcation of the crypts.
