Erythropoietin induces Ca²⁺ mobilization and contraction in rat mesangial and aortic smooth muscle cultures

Reportedly, recombinant human erythropoietin (rhEpo) can induce constriction of isolated resistance vessels. We have studied whether rhEpo affects cytosolic calcium concentration, [Ca²⁺](i), and contraction of cultured smooth-muscle cells grown from rat renal corpuscles and aortae. rhEpo at high dose (≥20 U/mL) induced a transient increase in [Ca²⁺](i) as detected by fura-2 fluorescence analysis. The number of cells responding with an increase in [Ca²⁺](i) was dose-dependent. No significant changes of [Ca²⁺](i) occurred when lower doses of rhEpo (<20 U/mL) were applied. The effect of Epo on contraction was studied by phase-contrast microscopy. The number of cells responding with contraction was dose-dependent, too (76% mesangial cells contracting at 200 U rhEpo per mL). The receptor mechanism of this unusual action of Epo still needs to be clarified.