A new mutation (db 3J) at the diabetes locus in strain 129/J mice

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Abstract
Monolayer cell cultures from pancreatic islets of aging 129/J strain diabetes (db 3J/db 3J) and lean littermate control mice were tested for differences in glucagon and insulin secretion in either serum-free Eagle's minimal essential medium (MEM) or Dulbecco's modified minimal essential medium (DMEM). There was a highly significant (pdb 3J/db 3J cultures in DMEM, mean medium glucagon levels increased 2.7-, 18-,and 32-fold above littermate normal culture levels at days 4, 6, and 8 respectively. In MEM, the two populations could not be discriminated on the basis of glucagon secretion. By contrast, insulin secretion over culture days showed a highly significant (pdb 3J/db 3J preparations secreting between 20 and 30 times as much insulin as controls in both media. Analysis revealed that the heightened secretory responsiveness of mutant A-cells in DMEM as compared to MEM was primarily elicited by the elevated DMEM amino acid concentration and specifically lysine (0.8 mmol/l in DMEM versus 0.4 mmol/l in MEM). In pulse-chase experiments using 14 day db 3J/db 3J cultures, incorporation of 3H-tryptophan into protein that eluted from Biogel P-10 columns in the native glucagon peak indicates that DMEM stimulated glucagon biosynthesis as well as secretion. This study reveals an augmented sensitivity of db 3J/db 3J A-cells to stimulation by basic amino acids in long-term culture.