In vitro Measurement of Electrolytes and Nutrients Transport through Intestinal Epithelium during Cholera Toxin Induced Secretion

Abstract

Cholera toxin and other bacterial toxins can induce electrogenic chloride (Cl-) secretion in the small
intestine resulting in secretory diarrhoea, when the colonic water reabsorption capacity is overwhelmed. The
mechanism underlying this phenomena is that, these toxins increase intracellular cGMP and/or cAMP level through
activation of guanylyl and adenylyl cyclase leading to the phosphorylation of the apical chloride channel (CFTR) and
electrogenic Cl- secretion as revealed in vitro by an increase in short-circuit current reflecting an increase in
electrolyte transport in the intestine. The aim of the study was to investigate the effects of D-(+) glucose on water and
electrolyte movements across rat jejunum after challenging with cholera toxin and dbcAMP (a lipophilic analog of
cAMP which readily crosses the basolateral membrane of small intestinal cells); and also to investigate whether the
magnitude of response to D-(+) glucose was related to the extent of secretion induced by dbcAMP. The measurement
of the ion transport across the unstripped rat jejunum was carried out using Ussing chambers. The response to D-(+)
glucose was studied in both CT-treated and untreated tissue; the results showed no significant difference between Isc
responses to D-(+) glucose in unstimulated and CT-stimulated rat jejunum (ΔIsc = 45.3 ± 12.9 μA/cm2 versus 38.9 ±
13.9 μA/cm2, n = 8), whereas, in the studies where tissues treated with dbcAMP instead of CT, results showed a small
but significant difference in D-(+) glucose response affected by dbcAMP (ΔIsc = 12.9 ± 4.7 μA/cm2 versus 24.0 ± 4.3
μA/cm2, n = 8).