Although P-cells form the largest cellular component of islets in most species—60 to 80 in rodents and 50 to 70 in humans (Cabrera et al. 2006; Clark et al. 1988; Elayat et al. 1995; Rahier et al. 1983a; Steiner et al. 2010)—the non-P-cells have important roles to play in intra-islet coordination and thus in the control of glucose homeostasis. It has been known for many years that the balance between insulin and the counter-regulatory hormone glucagon is of major importance in the fine control of glucose homeostasis and its disruption in diabetes (Unger et al. 1970; Unger and Orci 1975). The observations made with a glucagon receptor knockout mouse demonstrating the prevention of diabetes when glucagon signaling is impaired (Lee et al. 2011) highlighted the important role of a-cell secretion in vivo.
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