ABSTRACT
UTP-induced chloride secretion by the intestinal mucosa mounted in Ussing chambers was assessed by measurement of the short-circuit current (I(sc)) in the presence of phloridzin in the case of jejunum or amiloride in the case of colon to eliminate any contribution of electrogenic Na(+) movement to the net ionic transport. Since we have previously demonstrated the absence of chloride-secretory response to apical UTP in the jejunum from P2Y(4)-null mice, in the present study we studied the response to basolateral UTP in the jejunum and to either apical or basolateral UTP in the colon, in both P2Y(2)- and P2Y(4)-deficient mice. In the jejunum, the chloride-secretory response to basolateral UTP was partially reduced in both P2Y(2)- (40%) and P2Y(4)- (60%) null mice. In the colon, both apical or basolateral UTP increased the I(sc). That response was abolished in a chloride-free medium. The colonic chloride-secretory response to either basolateral or apical UTP was abolished in P2Y(4)-deficient mice, but not significantly affected in P2Y(2)-deficient mice. The chloride-secretory response to forskolin was potentiated by prior basolateral addition of UTP and this potentiation was abolished in P2Y(4)-null mice. The jejunum of mice homozygous for the DeltaF508 mutation of cystic fibrosis transmembrane conductance regulator was responsive to UTP, but the magnitude of that response was smaller than in the wild-type littermates. In conclusion, the P2Y(4) receptor fully mediates the chloride-secretory response to UTP in both small and large intestines, except at the basolateral side of the jejunum, where both P2Y(2) and P2Y(4) receptors are involved.
Subject(s)
Chlorides/metabolism , Intestinal Mucosa/metabolism , Receptors, Purinergic P2/metabolism , Animals , Colforsin/pharmacology , Colon/drug effects , Colon/metabolism , In Vitro Techniques , Intestinal Mucosa/drug effects , Jejunum/drug effects , Jejunum/metabolism , Mice , Mice, Knockout , Receptors, Purinergic P2/deficiency , Receptors, Purinergic P2/genetics , Receptors, Purinergic P2Y2 , Uridine Triphosphate/pharmacologyABSTRACT
Adenosine is known to stimulate chloride secretion by mouse jejunum. Whereas the receptor on the basolateral side is believed to be A2B, the receptor involved in the luminal effect of adenosine has not been identified. We found that jejuna expressed mRNA for all adenosine receptor subtypes. In this study, we investigated the stimulation of chloride secretion by adenosine in jejuna derived from mice lacking the adenosine receptors of A1 (A1R) and A2A (A(2A)R) or control littermates. The jejunal epithelium was mounted in a Ussing chamber, and a new method on the basis of impedance analysis was used to calculate the short-circuit current (I(sc)) values. Chloride secretion was assessed by the I(sc) after inhibition of the sodium-glucose cotransporter by adding phloridzin to the apical bathing solution. The effect of apical adenosine on chloride secretion was lost in jejuna from mice lacking the A1R. There was no difference in the response to basolaterally applied adenosine or to apical forskolin. Furthermore, in jejuna from control mice, the effect of apical adenosine was also abolished in the presence of 8-cyclopentyl-1,3-dipropylxanthine, a specific A1R antagonist. Responses to adenosine were identical in jejuna from control and A(2A)R knockout mice. This study demonstrates that A1R (and not A(2A)R) mediates the enhancement of chloride secretion induced by luminal adenosine in mice jejunum.
Subject(s)
Adenosine/physiology , Chlorides/physiology , Jejunum/physiology , Receptor, Adenosine A1/physiology , Receptors, Adenosine A2/physiology , Animals , Gene Expression/physiology , Jejunum/metabolism , Mice , Mice, Knockout , Receptor, Adenosine A1/genetics , Receptors, Adenosine A2/geneticsABSTRACT
The P2Y(4) receptor is responsive to UTP in human and to ATP and UTP in rodents. With the aim of identifying its pharmacotherapeutic interest, we generated P2Y(4)-null mice by a classic gene targeting method. The proportion of genotypes was consistent with X-linked Mendelian transmission. Gene inactivation was checked by the complete disappearance of P2Y(4) receptor mRNA from liver, stomach, and intestine. The P2Y(4)-null mice had a grossly normal behavior, growth, and reproduction. Chloride secretion by the jejunal epithelium was assessed in Ussing chambers by the measurement of the short circuit current in the presence of phlorizin. We show here that the UTP- and ATP-induced chloride secretory responses observed in wild-type mice are abolished in P2Y(4)-null mice. This is the first clearcut demonstration of a biological role of the P2Y(4) receptor.
