RESUMEN
1 Rat foetal distal lung epithelial cells were plated onto permeable supports where they became integrated into epithelial sheets that spontaneously generated short circuit current (ISC). 2 Apical ATP (100 microM) evoked a transient fall in ISC that was followed by a rise to a clear peak which, in turn, was succeeded by a slowly developing decline to a value below control. Apical UTP evoked an essentially identical response. 3 UDP and ADP were ineffective whilst ATP had no effect when added to the basolateral solution. These effects thus appear to be mediated by apical P2Y2 receptors. 4 The rising phase of the responses to ATP/UTP was selectively inhibited by anion transport inhibitors but persisted in the presence of amiloride, which abolished the inhibitory effects of both nucleotides. Thus, apical nucleotides appear to evoke a transient stimulation of anion secretion and sustained inhibition of Na+ absorption. 5 Basolateral isoprenaline (10 microM) elicited a rise in ISC but subsequent addition of apical ATP reversed this effect. Conversely, isoprenaline restored ISC to its basal level following stimulation with ATP. Apical P2Y2 receptors and basolateral beta-adrenoceptors thus allow their respective agonists to exert mutually opposing effects on ISC.
Asunto(s)
Células Epiteliales/metabolismo , Canales Iónicos/fisiología , Pulmón/metabolismo , Receptores Purinérgicos P2/fisiología , Adenosina Trifosfato/farmacología , Agonistas Adrenérgicos beta/farmacología , Animales , Calcio/metabolismo , Células Cultivadas , Inhibidores Enzimáticos/farmacología , Células Epiteliales/efectos de los fármacos , Canales Iónicos/antagonistas & inhibidores , Canales Iónicos/efectos de los fármacos , Isoproterenol/farmacología , Pulmón/efectos de los fármacos , Ratas , Receptores Purinérgicos P2Y2 , Tapsigargina/farmacología , Uridina Trifosfato/farmacologíaRESUMEN
ATP and UTP did not evoke [Ca2+]i signals in rat foetal lung epithelial cells grown on glass but elicited clear responses in cells grown into functionally polarised epithelia on permeable supports. Moreover, P2Y2 receptor mRNA could not be detected in cells on glass by the polymerase chain reaction but this mRNA species was clearly expressed by polarised cells. P2Y2 receptor expression thus appears to be a feature of the polarised phenotype.
Asunto(s)
Células Epiteliales/metabolismo , Pulmón/metabolismo , Receptores Purinérgicos P2/biosíntesis , Adenosina Trifosfato/farmacología , Animales , Calcio/fisiología , Polaridad Celular , Células Cultivadas , Células Epiteliales/efectos de los fármacos , Células Epiteliales/fisiología , Feto/metabolismo , Vidrio , Pulmón/citología , Pulmón/efectos de los fármacos , Pulmón/embriología , Ratas , Receptores Purinérgicos P2Y2 , Uridina Trifosfato/farmacologíaRESUMEN
Kainate inhibits the exchange of D-aspartate into guinea-pig cerebrocortical synaptosomes. Kainate inhibits the Ca2+-independent efflux of endogenous glutamate in the presence of a trapping system for the released amino acid but potentiates a Ca2+-independent net efflux of endogenous and labelled glutamate and aspartate in the absence of the trap. Dihydrokainate has a similar effect. No discrepancy is seen between the release of endogenous and exogenously accumulated amino acid. These results are consistent with the presence of a slow leak of glutamate or aspartate from the cytoplasm independent of the kainate-sensitive Na+-cotransport pathway. In the presence of the trap, glutamate effluxes by both pathways, whereas in the absence of the trap, the Na+-cotransport pathway opposes the leak. Neither in the presence or absence of the glutamate trap does kainate induce, inhibit, or otherwise affect the Ca2+-dependent release of endogenous glutamate. The results enable many of the apparent complexities in the presynaptic actions of kainate to be resolved.