Ba2+ inhibition of VIP- and A23187-stimulated Cl- secretion by T84 cell monolayers

Abstract

Addition of either 10(-8) M vasoactive intestinal polypeptide (VIP) or 10(-6) M A23187 to T84 cell monolayers, grown on permeable supports and mounted in Ussing chambers, stimulated net Cl- secretion. The effect of 10(-6) M A23187 on Cl- flux was consistently smaller than that observed with 10(-8) M VIP. In both cases the increase in net Cl- secretion accounted for the entire change in the observed short-circuit current (Isc). Since Cl- enters the cells through a basolaterally localized Na+-K+-Cl(-)-cotransport system (J. Clin. Invest. 75: 462, 1985), the fate of K+, which is cotransported with Cl- during VIP, and A23187-mediated Cl- secretion was explored. Unidirectional and net transepithelial 42K+ flux rates were negligible compared with 36Cl- flux rates (less than 4% of Cl- flux), indicating that little K+ was secreted along with Cl-. K+ recycling across the basolateral membrane was suggested from experiments in which 86Rb+ efflux (as a tracer for K+) was measured across the apical and basolateral membranes of 86Rb+ -preloaded monolayers under voltage-clamped conditions. In the absence of secretagogues, 86Rb+ efflux was 10-fold higher across the basolateral membrane than across the apical membrane. 86Rb+ efflux across the basolateral membrane was accelerated two- to threefold by addition of either VIP or A23187. In each case accelerated efflux was inhibited by 5 mM Ba2+. Cl- secretion induced by VIP or A23187 was also inhibited by serosal addition of Ba2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulated Cl transport, K and Cl permeability, and exocytosis in T84 cells.

“…There were no effects of forskolin on basolateral PK. It has been previously concluded that cAMP either activates (42) or has no effect (33) ( Fig. 9 A) and also toward the basolateral side (Fig.…”

Basolateral K+ channel involvement in forskolin‐activated chloride secretion in human colon

“…Forskolin has been shown to inhibit amiloride-sensitive Na¤ transport in rat colon (Ecke et al 1996) and further experiments are required to elucidate the exact effect of cAMP on Na¤ transport in intact human colonic epithelium. Apical chloride transport must be coupled to basolateral potassium transport if a favourable gradient for chloride secretion is to be maintained (Mandel et al 1986). There are believed to be two signal transduction pathways involved in human colonic secretion (Weyer et al 1985;Dharmsathaphorn & Pandol, 1987).…”

Cl- secretion induced by bile salts. A study of the mechanism of action based on a cultured colonic epithelial cell line.

“…Growth and maintenance of T84 cells, transepithelial electrolyte transport studies, and measurement of cAMP were performed as described earlier (14)(15)(16). Measurement of cGMP utilized a similar procedure to that described for cAMP except that a cGMP standard and cGMP antiserum were used instead of the cAMP standard and cAMP antiserum (22).…”

“…It is, therefore, difficult to define the mechanisms of bile acid induced electrolyte and water secretion at the cellular level based on in vivo studies or in vitro studies using isolated intestine. Recently, our laboratory has utilized a well-differentiated colonic epithelial cell line as a model system to study the mechanisms of secretagogueinduced Cl-secretion (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25). The uniformity of this model epithelium allows a less ambiguous characterization ofthe secondary messengers involved in the Cl-secretory process.…”