Mitogen-activated protein kinases (MAPKs) have been implicated in the signalling responses to hyposmotic shock (Zhang et al. 1998) and can be modulated by pro-inflammatory cytokines (Saklatvala et al. 1997). We aimed to determine whether MAPK pathways are involved in intracellular signalling events following hyposmotic shock applied to villous fragments of human placenta and whether cytokines modulate the role of MAPKs in this response.

Villous fragments of placentas collected at term following uncomplicated pregnancy were incubated in control Tyrode buffer (300 mosmol (kg H₂O)^-1) containing [³H] taurine (0.5 µCi ml^-1) for 90 min at 37 °C. Fragments were washed and exposed to sequential aliquots of control buffer at 10 min intervals for 3 Ω 10 min followed by experimental buffers (see below) for a further 6 Ω 10 min before being lysed in water to determine tissue [³H] taurine content. The % [³H] taurine efflux was calculated for each collection period. Treatments were compared by calculating the total % [³H] taurine efflux during the 60 min experimental period.

Basal % [³H] taurine efflux was unaffected by 0.6 nM interleukin 1β (IL-1β), 1.0 nM tumour necrosis factor-α (TNFα), SB203580 (SB: 25 µM, inhibitor of p38 MAPK) or PD98059 (PD: 25 µM, inhibitor of p44/42 MAPK pathways). Exposure to hyposmotic solution (190 mosmol (kg H₂O)^-1) over the experimental period significantly increased [³H] taurine efflux compared with control (Fig. 1A) . IL-1β and TNFα did not affect the hyposmotic response. Both PD and SB attenuated [³H] taurine efflux in hyposmotic conditions (Fig. 1B). IL-1β and TNFα restored the hyposmotic response in the presence of PD but neither cytokine modulated the inhibitory effect of SB.

Both IL-1β and TNFα restored hyposmotically stimulated [³H] taurine efflux in the presence of an inhibitor of p44/42 MAPK pathways. In contrast, these cytokines did not alter the attenuation of the hyposmotic effect seen with inhibition of p38 MAPK. These results demonstrate that p38 and p44/42 MAPK pathways have different sensitivities to the signalling milieu in placental villous tissue.

Saklatvala, J., Dean, J. & Finch, A. (1997). Biochem. Soc. Symp. 64, 63-67.

Zhang, Z., Yang, X.-Y. & Cohen, D.M. (1998). Am. J. Physiol. 275, C1104-1112.