Glucosamine inhibits angiotensin II-induced cytoplasmic [Ca.sup.2+] elevation in neonatal cardiomyocytes via protein-associated O-linked N-acetylglucosamine

We previously reported that glucosamine and hyperglycemia attenuate the response of cardiomyocytes 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 [Ca.sup.2+] entry into the cells; however, a direct link between HBP and intracellular [Ca.sup.2+] 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-GIcNAc) on ANG II-mediated changes in intracellular free [Ca.sup.2+] concentration ([Ca2 +]). We found that glucosamine blocked ANG II-induced [[[Ca.sup.2+]].sub.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 OGlcNAcase that increased O-GlcNAc levels without changing UDPG1cNAc concentrations, mimicked the effect of glucosamine on the ANG II-induced increase in [[[Ca.sup.2+]].sub.i]. An inhibitor of O-GlcNActransferase, 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 [[[Ca.sup.2+]].sub.i]. These data support the notion that changes in O-GlcNAc levels mediated via increased HBP flux may be involved in the regulation of [[[Ca.sup.2+]].sub.i] homeostasis in the heart. hypertrophy; left ventricle; calcium channels; calcium signaling