Change of endothelin receptor subtype in the MEG-01 human megakaryoblastic cell line

The aim of this investigation was to determine whether the endothelin receptor subtype of a megakaryoblastic cell line (MEG-01) changes during culture passages as cells undergo maturation and differentiation. On early-passage cells, binding of [ 125 I ]endothelin-1 was completely inhibited by 1 μM BQ 123 (cyclo-[ d -tryptophanyl- d -aspartyl–prolyl- d -valyl–leucyl]), but not by sarafotoxin 6C. Also the endothelin-1-enhancing effect on [Ca2+]i was prevented by BQ 123, whereas sarafotoxin 6C had no effect on [Ca2+]i. In late-passage cells, endothelin ETB analogs, unlike endothelin ETA analogs, competed with binding of [ 125 I ]endothelin-1. Endothelin ETB receptor agonists increased [Ca2+]i while the endothelin-1-induced response was inhibited by BQ 788 ([N-[(2R,6S)-2,6-dimethyl-piperidinocarbonyl]-4-methyl- d -leucyl]-[Nω-(methoxycarbonyl)- d -tryptophanyl]- d -norleucine), but not by BQ 123, although both endothelin ETA and ETB receptor mRNAs were expressed, as shown by reverse transcriptase–polymerase chain reaction. These results demonstrate that in MEG-01 cells switch from expression of endothelin ETA to expression of ETB receptors during culture. The data also suggest that late-passage MEG-01 cells look like platelets, in terms of endothelin receptor subtype.