Effects of low density lipoprotein on cytosolic [Ca++] in cultured rat mesangial cells.

BACKGROUND

Recently, a low density lipoprotein (LDL) receptor has been identified in mesangial cells. However, the nature of intracellular signals in mesangial cells after exposure to LDL is unclear.

METHODS

We studied the effect of LDL on cultured rat mesangial cell [Ca++]i using spectrofluorometry.

RESULTS

Addition of LDL (15 micrograms/mL) produced a rapid, transient, and dose-dependent rise in [Ca++]i within seconds, returning to baseline in 6 minutes. No further rise was observed at higher LDL concentrations. No significant rise in [Ca++]i was observed with LDL in cells placed in a Ca(++)-free medium. The [Ca++]i rise was greatly attenuated in magnitude and duration when lanthanum was used. In contrast, verapamil failed to block the LDL-induced rise in [Ca++]i. Addition of LDL did not alter production of inositol 1,4,5-triphosphate (IP3) by mesangial cells.

CONCLUSIONS

Low density lipoprotein caused a transient rise in [Ca++]i in cultured rat mesangial cells. The observed rise in [Ca++]i was largely caused by influx of extracellular Ca++ through receptor-gated channels. Mobilization from intracellular stores and activation of IP3 were not involved. The rise in [Ca++]i may mediate the effects of LDL on mesangial cell function.