Role Of Calcineurin In Regulation Research Articles

Ca 2+-dependent modulation of single human cardiac L-type calcium channels by the calcineurin inhibitor cyclosporine

Objective. – Activity of single L-type calcium channels (LTCC) is enhanced in human failing myocardium (Circulation 98 (1998) 969.), most likely due to impaired dephosphorylation. Protein phosphatase 2B (calcineurin) has recently been shown to be involved in heart failure pathophysiology. We now focus on the regulation of single LTCC by calcineurin that were prevented by Ca 2+-free experimental conditions in our previous study. Methods. – Single LTCC currents were recorded in myocytes from human atrium and ventricle. Charge carriers were 70 mM Ba 2+, or a mixture of 30 mM Ca 2+ and 60 mM Ba 2+ to facilitate Ca 2+ permeation through recorded channels. The calcineurin inhibitor cyclosporine (10 μM) was used to reveal a putative role for calcineurin in regulation of LTCC. Results. – A mixture of Ca 2+ and Ba 2+ as charge carriers allowed for Ca 2+ permeation through recombinant human embryonic kidney cells and native (atrial and ventricular) human cardiac LTCC. With only Ba 2+ as the charge carrier, activities of both ventricular and atrial LTCC were strongly decreased by cyclosporine. In contrast, channel activity remained constant when Ca 2+ permeation was provided. In the presence of thapsigargin and (S)-BayK 8644, cyclosporine here even increased channel activity. Conclusions. – We propose a dual cyclosporine effect on human cardiac LTCC. A non-specific inhibitory effect prevails with Ba 2+ permeation but can be compensated or overcome by a specific Ca 2+-dependent stimulation with Ca 2+ permeation. More complete restoration of physiological Ca 2+ movements (e.g., Ca 2+ release from sarcoplasmic reticulum) will help to define even more precisely the involvement of calcineurin in regulation of human cardiac LTCC.

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 calcineurin (CN) has been implicated in the Ca2+-dependent inactivation of Ca2+ 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 carrying the catalytic subunit of human PP2Bbeta3. Relative to mock-transfected (wild-type) controls, cells overexpressing calcineurin showed dramatically reduced high-voltage-activated Ca2+ currents which were recoverable by the inclusion of 1 microM 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-activated Ca2+ currents revealed that the kinetics of inactivation were significantly accelerated in cells overexpressing calcineurin. Following the delivery of a train of depolarizing pulses in experiments designed to produce large-scale Ca2+ influx across the cell membrane, Ca2+-dependent inactivation 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 microM FK506. These data support a role of calcineurin in the negative feedback regulation of Ca2+ entry through voltage-operated Ca2+ channels.

Role of calcineurin in regulation of high voltage-activated calcium channel activity

In the Review, personal data of the Author and the data of other experimenters on calcium/calmodulin-dependent protein phosphatase-2B (calcineurin) are summarized and analyzed; the role of this enzyme in regulation of the calcium channel activity in the membrane of excitable cells is discussed. A two-phase mechanism of Ca-dependent suppression of the activity of Ca channels in the molluscan neurons is described in details. Special attention is paid to the analysis of changes in the activity of Ca channels in the transfected hybrid cells overexpressing calcineurin.