TBK1 and diabetes mellitus: Overall, the studies of Na+,K+-ATPaseactivity have delineated a stimulatory signalling action of C-peptide atphysiological concentrations dependent on intracellular Ca2+ andPKC, and sensitive to PTX suggesting the presence of a GPCR for C-peptide.Replacement of C-peptide in diabetic animals and patients with diabetes has asalutary effect on Na+,K+-ATPase activity in a variety oftissues affected by diabetic complications.