Signalling mechanisms involved in C‐peptide‐mediated inhibition of low O2‐induced ATP release from human erythrocytes

Background and objectivesIn vivo, insulin is released with connecting peptide (C-peptide) which has recently been shown to have biological activity. When erythrocytes are exposed to reduced oxygen (O2) tension, they release O2 as well as the vasodilator ATP enabling them to participate in the appropriate distribution of vascular perfusion and, thereby, O2 supply. Low O2-induced ATP release is absent in erythrocytes of humans with type 2 diabetes (DM2), but this response is restored by co-administration of physiological concentrations of insulin and C-peptide. However, either C-peptide or insulin, when administered alone, inhibits low O2-induced ATP release from healthy human erythrocytes. Here, we investigated the mechanism(s) by which C-peptide inhibits this physiological ATP release from human erythrocytes.MethodsErythrocytes from healthy humans (n = 21) or humans with DM2 (n = 4) were incubated with C-peptide in the absence or presence of inhibitors of either protein kinase C alpha (PKCα) or soluble guanylyl cyclase (sGC). Erythrocytes were then exposed to low O2, and ATP release was determined.ResultsIn healthy human erythrocytes, C-peptide inhibited ATP release in response to low O2. Preincubation with either Go6976, a PKCα inhibitor, or ODQ, a sGC inhibitor, prevented this effect of C-peptide. In addition, C-peptide alone did not rescue low O2-induced ATP release from DM2 erythrocytes.ConclusionAdministration of C-peptide in excess of levels present under physiological conditions or the combination of C-peptide and insulin at ratios that exceed those observed physiologically to insulin-deficient individuals can be detrimental for low O2-induced ATP release from human erythrocytes and could, consequently, interfere with optimal O2 delivery to skeletal muscle.