Norepinephrine stimulates creatine transporter activity in cardiomyocytes via β‐adrenergic activation: implications for heart failure energetics

Abstract

Creatine (Cr), phosphocreatine (PCr) and creatine-kinases constitute an energy shuttle between mitochondria and sites of high energy consumption that maintains ATP levels in cardiomyocytes. Profound alterations in Cr and PCr levels are observed in heart failure (HF). Cardiomyocytes are not able to synthesize Cr, thus depend on transport via the Cr transporter (CrT) to maintain intracellular Cr stores. Cr transport regulation and how it is affected in HF is not yet clearly understood. We hypothesized that in cardiomyocytes CrT is regulated by β-adrenergic signaling, and that β-adrenergic signaling alterations are involved in depletion of Cr stores seen in HF. 14C-Cr uptake in rat neonatal cardiomyocytes is increased by 46% after incubation with 10μM isoproterenol (ISO). HL-1cells expressing the human CrT and incubated in 100μM ISO for 24 hours increased 14C-Cr uptake by 50%. This effect was prevented by preincuabtion with the β1-β2 antagonist propranolol. A 60% increase in 14C-Cr uptake was seen in HL-1 cells following incubation with 100μM norepinephrine. Kinetic analysis showed changes in Km and V max, suggesting increased CrT protein availability and substrate affinity. CrT protein content is increased in HL-1 cells following 48hr incubation with ISO. Our findings suggest the existence of a coupling mechanism between adrenergic activation (e.g., increased work load) and energetic status of cardiomyocytes.