MORPHOLOGICAL AND FUNCTIONAL-CHARACTERIZATION OF BETA-TC-6 CELLS - ANINSULIN-SECRETING CELL-LINE DERIVED FROM TRANSGENIC MICE

Morphological analysis of hormone content and functional assessment of hormone secretion were conducted in beta TC-6 cells, an insulin-secre ting cell. line derived from transgenic mice expressing the large T-an tigen of simian virus 40 (SV40) in pancreatic beta-cells. We observed by immunohistochemistry and confocal microscopy that beta TC-6 cells c ontain abundant insulin and small amounts of glucagon and somatostatin (SRIF), Glucagon usually co-localized with insulin, whereas cells con taining SRIF did not contain insulin or glucagon, Static incubation an d perifusion experiments demonstrated that beta TC-6 cells at passage 30-45 secrete insulin in response to glucose, In static incubations, m aximal stimulation was achieved for glucose concentrations > 2.8 mmol/ l glucose, and the half-maximal effect was observed at 0.5 mmol/l, Max imal stimulation was four times greater than HIT-T15 cells at passage 72-81, although HIT cells had a greater response over their basal leve ls, The magnitude of the insulin response to glucose in perifusion was 1,734 +/- 384 pmol . l(-1). min acid was 4.6-fold greater in the pres ence of 3-isobutyl-1-methylxanthine. Low amounts of glucagon were rele ased in response to amino acids. Epinephrine (EPI), and to a lesser ex tent SRIF, inhibited phasic glucose-induced insulin secretion, A major portion of these inhibitory effects was mediated by pertussis toxin-s ensitive substrates. Immunoblots detected the presence of the G-protei ns Gi alpha 2, Gi alpha 3, and Go alpha 2. These results indicate that beta TC-6 cells are a glucose-responsive cell line in which insulin e xocytosis is physiologically regulated by EPI and SRIF through Gi/Go-m ediated mechanisms.