Inhibition of calcineurin in mouse ventricular myocytes increased the amplitude and decay rate of calcium transients and prolonged action potentials, effects that were prevented by PKA inhibition.
We examined the role of the Ca(2+)-regulated protein phosphatase calcineurin in controlling Ca(2+) signalling in mouse ventricular myocytes. Membrane currents and voltage were measured in single myocytes using the patch-clamp technique. Cytoplasmic Ca(2+) concentration (Ca(2+)(i)) was measured in cells loaded with the fluorescent Ca(2+) indicators fluo-4 or fura-2 using a confocal or epifluorescence microscope. Inhibition of calcineurin with cyclosporin A (CsA, 100 nM) or the calcineurin auto-inhibitory peptide (CiP, 100 microM), increased the amplitude and rate of decay of the evoked Ca(2+)(i) transient and also prolonged the action potential (AP) of ventricular myocytes to a similar extent. The effects of CsA (100 nM) and 100 microM CiP on the Ca(2+)(i) transient and AP were not additive. Calcineurin inhibition did not modify the K(+) currents responsible for repolarisation of the mouse ventricle. Instead, inhibition of calcineurin increased the amplitude of the Ca(2+) current (I(Ca)) and the evoked calcium transient normalized to the I(Ca). Calcium sparks, which underlie the Ca(2+)(i) transient, had a higher frequency and amplitude, suggesting an elevation of SR calcium load. Inhibition of protein kinase A (PKA) prevented the effects of calcineurin inhibition, indicating that calcineurin opposes the actions of PKA. Finally, immunofluorescence images suggest that calcineurin and PKA co-localize near the T-tubules of ventricular myocytes. We propose that calcineurin and PKA are co-localized to control Ca(2+) influx through calcium channels and calcium release through ryanodine receptors.
Santana et al. (Mon,) reported a other. Calcineurin inhibition (cyclosporin A or calcineurin auto-inhibitory peptide) was evaluated on Amplitude and rate of decay of evoked [Ca(2+)](i) transient and action potential duration. Inhibition of calcineurin in mouse ventricular myocytes increased the amplitude and decay rate of calcium transients and prolonged action potentials, effects that were prevented by PKA inhibition.