A modulatory role for protein phosphatase 2B (calcineurin) in the regulation of Ca2+ entry

The Ca2+/calmodulin-dependent protein phosphatase 2B (PP2B) also known as c alcineurin (CN) has been implicated in the Ca2+-dependent inactivation of C a2+ channels in several cell types. To study the role of calcineurin in the regulation of Ca2+-channel activity, phosphatase expression was altered in NG108-15 cells by transfection of sense and antisense plasmid constructs c arrying the catalytic subunit of human PP2B beta(3). Relative to mock-trans fected (wild-type) controls, cells overexpressing calcineurin showed dramat ically reduced high-voltage-activated Ca2+ currents which were recoverable by the inclusion of 1 mu m FK506 in the patch pipette. Conversely, in cells with reduced calcineurin expression, high-voltage-activated Ca2+ currents were larger relative to controls. Additionally in these cells, low-voltage- activated currents were significantly reduced. Analysis of high-voltage-act ivated Ca2+ currents revealed that the kinetics of inactivation were signif icantly accelerated in cells overexpressing calcineurin. Following the deli very of a train of depolarizing pulses in experiments designed to produce l arge-scale Ca2+ influx across the cell membrane, Ca2+-dependent inactivatio n of high-voltage-activated Ca2+ currents was increased in sense cells, and this increase could be reduced by intracellular application of 1 mm BAPTA or 1 mu m FK506. These data support a role of calcineurin in the negative f eedback regulation of Ca2+ entry through voltage-operated Ca2+ channels.