The gut microbiota metabolite phenylacetylglycine regulates cardiac Ca signaling by interacting with adrenergic receptors.

Phenylacetylglutamine (PAGln) and phenylacetylglycine (PAGly) are small molecules derived from the metabolism of phenylalanine by gut microbiota. Elevated levels of PAGln and PAGly in serum have been associated with increased risks for cardiovascular diseases. It has been suggested that PAGln and PAGly reduce cardiac contraction by blunting the adrenergic response during sympathetic stimulation. However, little is known whether the effect of PAGln and PAGly on the heart function is associated with an alteration of intracellular Ca homeostasis. Here, we studied the effect of PAGly on Ca regulation in mouse ventricular myocytes, as PAGly is the predominant phenylalanine metabolite in rodent's serum. Analysis of cytosolic Ca dynamics revealed that PAGly (100 μM) increases action potential-induced Ca transients and sarcoplasmic reticulum (SR) Ca load. These effects of PAGly were significantly smaller than those produced by the adrenergic receptor agonist isoproterenol (ISO; 0.1 μM). The adrenergic receptor blocker propranolol (10 μM) and the protein kinase A (PKA) inhibitor H89 (10 μM) prevented the PAGly effects on intracellular Ca dynamics. Further analysis of Ca regulation revealed that pretreatment of cardiomyocytes with PAGly reduced the stimulatory effect of ISO on intracellular Ca dynamics. Concurrently, PAGly did not produce any stimulatory effects on intracellular Ca in the presence of ISO. In conclusion, PAGly regulates intracellular Ca dynamics in ventricular myocytes by activating the adrenergic receptor-mediated signaling, but less efficiently than selective adrenergic agonists. By interacting with adrenergic receptors, PAGly can partially blunt the stimulatory effect of adrenergic receptor agonists.