Background: The most widely used immunosuppressive drug for preventing graft rejection and treating autoimmune diseases is currently cyclosporine A (CsA). However, CsA also causes vasoconstriction, which is considered to be at the origin of CsA-induced nephrotoxicity and hypertension. To evaluate the cellular basis for these side effects, we studied the influence of CsA on the regulation of the free cytosolic Ca2+ concentration ([Ca2+]c) in cultured human vascular smooth muscle cells (SMCs).
Methods: SMCs were isolated from the medial layer of human aorta. [Ca2+]c regulation was studied by fluorimetry with fura 2 and by measuring 45Ca2+ effluxes. Angiotensin II (Ang II) receptors were detected by [125I]Ang II binding.
Results: Pretreatment of human SMCs for 24 hours with CsA in its therapeutic concentration range (0. 1 to 10.0 microM) had no effect on basal [Ca2+]c, but increased the [Ca2+]c elevation and 45Ca2+ efflux when cells were stimulated with Ang II. Half-maximal effects occurred at approximately 1 microM CsA. The CsA effects on [Ca2+]c were accompanied by a nearly twofold increase in Ang II receptor number, whereas no change in affinity to Ang II was observed. CsA did not alter endothelin-1- or thapsigargin-induced 45Ca2+ efflux. Increases in both Ca2+ responses and [125I]Ang II binding were attenuated by the transcriptional inhibitor actinomycin D. The effects of CsA did not appear to be mediated by calcineurin inhibition because cyclosporine H, which is not immunosuppressive, also increased the Ang II-induced 45Ca2+ efflux.
Conclusion: These data suggest that CsA preferentially up-regulates the transcription of Ang II receptors, which very likely leads to vasoconstriction in vivo and could be at the origin of CsA-induced hypertension and nephrotoxicity in humans.