Adriamycin impairs the contraction of mesangial cells through the inhibition of protein kinase C and intracellular calcium

The effects of adriamycin on the contractile function of cultured mesangial cells were measured by the changes in planar surface area in response to treatment with agonists. Incubation of mesangial cells with adriamycin (0.2 μg/ml) for 24 h significantly decreased the contractile responses to the calcium channel activator BAY K 8644 (1 μM) and to the PKC activator PMA (1 μM). Intracellular calcium concentration ([Ca²⁺]_i), measured by changes in fura 2 levels in response to ATP (0.1 mM), was significantly inhibited in adriamycin-treated mesangial cells compared with control cells. In the absence of extracellular calcium, treatment with ionomycin (0.1 mM) or thapsigargin (10 μM) resulted in a significantly smaller increase in [Ca²⁺]_i in adriamycin-treated mesangial cells compared with control, suggesting an important role of the endoplasmic reticulum in the effects of adriamycin. Using PKC-specific antibodies, adriamycin significantly decreased the cytosolic and membranous fractions of PKC-α in mesangial cells to 75 ± 6 and 70 ± 12% of control, respectively. The PKC activity of mesangial cells was also significantly inhibited after incubation with adriamycin for 24 h. In conclusion, adriamycin induces hypocontractility of mesangial cells, which may mediate this effect by inhibiting PKC-α and [Ca²⁺]_i.