Glucosamine inhibits angiotensin II-induced cytoplasmic Ca2+ elevation in neonatal cardiomyocytes via protein-associated O-linked N-acetylglucosamine

We previously reported that glucosamineand hyperglycemia attenuate the response of to inositol 1,4,5-trisphosphate-generating agonists such as ANG II. This appears to be related to an increase in flux through the hexosamine biosynthesis pathway (HBP) and decreased Ca2+ entry into the cells; however, a direct link between HBP and intracellular Ca2+ homeostasis has not been established. Therefore, using neonatal rat ventricular myocytes, we investigated the relationship between glucosamine treatment; the concentration of UDP-N-acetylglucosamine (UDP-GlcNAc), an end product of the HBP; and the level of protein O-linked N-acetylglucosamine (O-GlcNAc) on ANG II-mediated changes in intracellular free Ca2+ concentration ([Ca2+](i)). We found that glucosamine blocked ANG II-induced [Ca2+](i) increase and that this phenomenon was associated with a significant increase in UDP-GlcNAc and O-GlcNAc levels. O-(2-acetamido-2-deoxy-(D)-glucopyranosylidene)amino-N-phenylcarbamate, an inhibitor of O-GlcNAcase that increased O- GlcNAc levels without changing UDPGlcNAc concentrations, mimicked the effect of glucosamine on the ANG II-induced increase in [Ca2+](i). An inhibitor of O-GlcNAc-transferase, alloxan, prevented the glucosamine-induced increase in O- GlcNAc but not the increase in UDP-GlcNAc; however, alloxan abrogated the inhibition of the ANG II-induced increase in [Ca2+](i). These data support the notion that changes in O- GlcNAc levels mediated via increased HBP flux may be involved in the regulation of [Ca2+](i) homeostasis in the heart.