Protein carbonylation causes sarcoplasmic reticulum Ca2+ overload by increasing intracellular Na+ level in ventricular myocytes.

Diabetes is commonly associated with an elevated level of reactive carbonyl species due to alteration of glucose and fatty acid metabolism. These metabolic changes cause an abnormality in cardiac Ca regulation that can lead to cardiomyopathies. In this study, we explored how the reactive α-dicarbonyl methylglyoxal (MGO) affects Ca regulation in mouse ventricular myocytes. Analysis of intracellular Ca dynamics revealed that MGO (200 μM) increases action potential (AP)-induced Ca transients and sarcoplasmic reticulum (SR) Ca load, with a limited effect on L-type Ca channel-mediated Ca transients and SERCA-mediated Ca uptake. At the same time, MGO significantly slowed down cytosolic Ca extrusion by Na/Ca exchanger (NCX). MGO also increased the frequency of Ca waves during rest and these Ca release events were abolished by an external solution with zero [Na] and [Ca]. Adrenergic receptor activation with isoproterenol (10 nM) increased Ca transients and SR Ca load, but it also triggered spontaneous Ca waves in 27% of studied cells. Pretreatment of myocytes with MGO increased the fraction of cells with Ca waves during adrenergic receptor stimulation by 163%. Measurements of intracellular [Na] revealed that MGO increases cytosolic [Na] by 57% from the maximal effect produced by the Na-K ATPase inhibitor ouabain (20 μM). This increase in cytosolic [Na] was a result of activation of a tetrodotoxin-sensitive Na influx, but not an inhibition of Na-K ATPase. An increase in cytosolic [Na] after treating cells with ouabain produced similar effects on Ca regulation as MGO. These results suggest that protein carbonylation can affect cardiac Ca regulation by increasing cytosolic [Na] via a tetrodotoxin-sensitive pathway. This, in turn, reduces Ca extrusion by NCX, causing SR Ca overload and spontaneous Ca waves.