Retinoids modulate P2Upurinergic receptor-mediated changes in transcervical paracellular permeability.

In human cervical cells, extracellular ATP induces an acute decrease in the resistance of the lateral intercellular space, the phase I response, followed by a delayed increase in tight junctional resistance, the phase II response. These responses depend on vitamin A because incubation of cells in retinoid-free medium (RFM) abolished both responses. Treatment with retinoic acid restored the phase I response in full, but the amplitude of the phase II response was restored only partly. Shorter incubations and lower concentrations of retinoic acid [half-maximal effective concentration ( K ½) = 0.1 μM] were required for restoring the phase I response than were required for reversing the phase II response ( K ½ = 1 μM). The phase I response could be restored by ligands that bind to either retinoic acid receptors (RARs) or retinoid X receptors, but only RAR agonists had an effect on phase II response. RFM had no effect on decreases in resistance induced by ionomycin, but it attenuated phase II-like increases in resistance induced by KCl or by 1,2-dioctanoyl- sn-diglycerol (diC8). Actinomycin D blocked phase IIresponse but not phase I response or the responses to ionomycin, KCl, or diC8. These results suggest that retinoids act on cervical cells via distinct retinoid receptor mechanisms and modulate phase I and phase II changes in resistance by regulating distinct signal mechanisms.