Adult human mesangial cells (HMCs) express endothelin-B-receptors which mediate endothelin-1-induced cell growth

Endothelin (ET) receptor antagonists are nephroprotective in renal damage m odels of the rat. It is unknown whether ET receptor antagonists are also be neficial in human renal diseases. Major differences exist between the ET sy stems in rats and humans, therefore this study was designed to characterize the ET receptors expressed on human adult mesangial cells (HMCs). HMCs cul tures are a surrogate model for the development of glomerulosclerosis. Bind ing experiments with [I-125]ET-1 in the presence or the absence of the test compounds [endothelin-1, -3 (ET-1, ET-3), sarafotoxin 6c (S6c), or BQ123] revealed an affinity (IC50 values) of 10.5 nm for ET-1 and 87.6 nm for ET-3 . The affinities of the ETB agonist S6c and the ETA antagonist BQ123 were 8 5.9 nm and > 10 mum, respectively. Thus, the ET receptor on HMCs shows an E TB-like pharmacology, but in contrast to the classical ETB-receptor the aff inities are low. No affinity for BQ123 up to > 10 mum excludes the presence of ETA-receptors. Functional studies using microfluorimetry (fura-2 method ) showed comparable biphasic calcium signals induced by 10 nm ET-1, ET-3 an d S6c. This effect could not be inhibited by BQ123, but by the ETB antagoni st BQ788. Reverse transcriptase polymerase chain reaction (RT-PCR) studies under different culture conditions showed that both ETA- and ETB-receptor m RNAs are expressed in HMCs. The amount of ETA-receptor mRNA increased 2.7-f old and that of the ETB-receptor mRNA 7.1-fold after stimulation with 10% f etal calf serum (FCS). ET-1, ET-3 and S6c stimulated HMCs growth (ET-1 > S6 c > ET-3), but the magnitude of the effect of ET-1 is lower than reported i n rat mesangial cells (rat MCs). The effect on HMCs growth could be inhibit ed by BQ788, but not by BQ123. Our data provide evidence for the expression of ETB-receptors on HMCs that are functionally active. This finding differ s from the ET receptor expression in rat MCs as reported by others.