A potent immunosuppresant and in vitro T cell proliferation blocker. It disrupts calcineurin-mediated signal transduction in T-lymphocytes. It interacts with its FK506-binding protein-12 (FKBP-12), leading to increase in the release of sarcoplamic reticulum-derived calcium. FK506 and rapamycin, but not cytosporin inhibit aldosterone-stimulated sodium transport in A6 cells.