DIRECT INTERACTIONS BETWEEN PLATELETS AND CULTURED RAT MESANGIAL CELLS

Platelets seem to be involved in the pathogenesis of some kidney disea ses, but the exact relationships between platelets and the changes in renal function are incompletely known. Mesangial cells (MC) were incub ated with platelet-supernatants (PS) and cellular surface area (CSA) a nd myosin light-chain phosphorylation (MLCP) were measured. CSA of PS- incubated MC (PS-MC) significantly diminished, as compared to control MC (70 +/- 6% vs. 100 +/- 5%). PS induced a significant increase in ML CP with respect to control cells (150 +/- 23% vs. 100 +/- 18%). When p latelets were pretreated with indomethacin, the PS-dependent contracti on was abolished. Pretreatment with sulotroban (SU) or BN-52021 (BN), a thromboxane A2 (TXA2) and a platelet-activating factor (PAF) recepto r blocker respectively, also completely blocked the PS effects. In oth er experiments, platelets were activated with thrombin (T), adding the so obtained PS to MC. Moreover, cells were also preincubated with T a nd then added PS. No changes in CSA were observed in either case. It m ay be concluded that PS contracted cultured MC, and these changes coul d be related to the decreased glomerular filtration rate (GFR) observe d in some diseases in which platelets seem to be involved. TXA2 and PA F may be responsible for this effect. In contrast, T incubation inhibi ted the effect of PS, perhaps through a direct relaxing effect of T in MC.