Mechanisms of Glucosamine‐Mediated Relaxing Responses in Isolated Rat Aortic Rings

Abstract

Glucosamine (GlcN) has been shown to block capacitative Ca2+ entry, also referred to as store‐operated Ca2+ entry (SOCE), in rat cardiomyocytes in response to phenylephrine (PHE). We hypothesized that GlcN would suppress SOCE in smooth muscle cells and lower intracellular [Ca2+] in PHE‐contracted rat aortic rings leading to vasorelaxation. In the wire‐myograph, relaxing responses to GlcN (0.01 – 30 mM) were assessed in PHE‐contracted rat aortic rings. GlcN relaxed endothelium‐denuded (−E) aortic rings with a sensitivity (pEC50) of 2.73 ± 0.09. The cell impermeable and osmotic control L‐ glucose (L‐Glc; 0.01 – 30 mM) did not result in arterial relaxations. Inhibition of the sarcoendoplasmic reticulum (ER) Ca2+‐ATPase (SERCA) results in Ca2+ depletion in the ER, which activates SOCE. The selective SERCA inhibitors thapsigargin (10 μM) and cyclopiazonic acid (50 μM) both significantly suppressed relaxations to GlcN in −E aortic rings. In Ca2+ depleted –E aortic rings, re‐titration of CaCl2 (0.01 – 5 mM) resulted in a lower sensitivity to CaCl2 in the presence of 5 mM GlcN compared to L‐Glc. Pre‐incubation with the SOCE inhibitor SKF96365 (10 μM) reduced sensitivity to CaCl2to comparable levels for both GlcN and L‐Glc. The present findings demonstrate that GlcN acts via an endothelium‐independent and cGMP‐dependent mechanism that inhibits SOCE to lower smooth muscle cell [Ca2+]i with subsequent vasorelaxation.