Effects of Palmitate on Ca²⁺ Handling in Adult Control and ob/ob Cardiomyocytes

Abstract

Obesity and insulin resistance are associated with enhanced fatty acid utilization, which may play a central role in diabetic cardiomyopathy. We now assess the effect of the saturated fatty acid palmitate (1.2 mmol/l) on Ca²⁺ handling, cell shortening, and mitochondrial production of reactive oxygen species (ROS) in freshly isolated ventricular cardiomyocytes from normal (wild-type) and obese, insulin-resistant ob/ob mice. Cardiomyocytes were electrically stimulated at 1 Hz, and the signal of fluorescent indicators was measured with confocal microscopy. Palmitate decreased the amplitude of cytosolic Ca²⁺ transients (measured with fluo-3), the sarcoplasmic reticulum Ca²⁺ load, and cell shortening by ∼20% in wild-type cardiomyocytes; these decreases were prevented by the general antioxidant N-acetylcysteine. In contrast, palmitate accelerated Ca²⁺ transients and increased cell shortening in ob/ob cardiomyocytes. Application of palmitate rapidly dissipated the mitochondrial membrane potential (measured with tetra-methyl rhodamine-ethyl ester) and increased the mitochondrial ROS production (measured with MitoSOX Red) in wild-type but not in ob/ob cardiomyocytes. In conclusion, increased saturated fatty acid levels impair cellular Ca²⁺ handling and contraction in a ROS-dependent manner in normal cardiomyocytes. Conversely, high fatty acid levels may be vital to sustain cardiac Ca²⁺ handling and contraction in obesity and insulin-resistant conditions.