(A) Overview of expression and post-transcriptional processing of proglucagon in the α cell, also showing differential processing in other tissues (boxed inset). Abbreviations: cAMP, cyclic adenosine monophosphate; PKC, protein kinase C; TSS, transcription start site; UTR, untranslated region; GRPP, glicentin-related pancreatic polypeptide; IP, intermediate peptide; GLP, glucagon-like peptide; (B) Schematic of major human α cellular components, including neuroendocrine cell surface receptors. For effects of these receptors on α cell physiology, see Table 3. Abbreviations: K+, potassium; KATP, ATP-sensitive potassium channel; ADORA1, adenosine A1 receptor; AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; SSTR2, somatostatin receptor 2; INSR, insulin receptor; Ca2+, calcium; Na+, sodium; GABA, gamma-aminobutyric acid; Eph, ephrin; 5-HT, serotonin.