Insulin inhibits ATP release from human erythrocytes

Abstract

Erythrocytes (RBCs) release ATP via a signal transduction pathway involving both the G protein Gi and increases in cAMP. In non-erythroid tissue, insulin has been shown to stimulate phosphodiesterase 3 (PDE3) resulting in the hydrolysis of cAMP. Although PDE activity within the RBC has not been fully characterized, incubating human RBCs with a PDE 3 inhibitor, cilostazol (100 μM), increased cAMP in these cells from 1.5±0.1 to 2.0±0.3 pmole (normalized to 5x108 RBC/mm3, n=12, P<0.05). Here, using mastoparan 7 (MAS 7) to activate Gi, we investigated the hypothesis that insulin reduces cAMP in RBCs and, thereby, decreases ATP release. RBCs from healthy humans were incubated with MAS 7 in the presence or absence of insulin (1 μM). Importantly, insulin alone had no effect on basal levels of cAMP or ATP release. In contrast, ATP release induced by MAS 7 (10 μM) was decreased in the presence of insulin from 1.2±0.2 to 0.78±0.1 μM (normalized to 4x105 RBC/mm3, n=5, P<0.05). Furthermore, the amount of cAMP in RBCs was decreased in the presence of insulin from 2.9±0.4 to 2.2±0.3 pmole (normalized to 5x108 RBC/mm3, n=6, P<0.05). These studies support the hypothesis that insulin, by decreasing cAMP accumulation, limits ATP release from RBCs in response to activation of Gi. These findings also suggest that PDE3 activity is present in human RBCs. One interpretation of these results is that increased plasma insulin levels in humans with insulin resistance could be detrimental to the ATP release from RBCs and could contribute to vascular complications in these individuals. Supported by NIH grants HL-64180 and HL-51298 and an ADA Innovation Award.