Refractoriness to growth hormone is associated with increased intracellular calcium in rat adipocytes
Department of Physiology
Adipose Tissue; Animals; Calcium; Cells, Cultured; Fluorescent Dyes; Fura-2; Growth Hormone; Insulin; Male; Microscopy, Fluorescence; Oxytocin; Rats; Rats, Inbred Strains
Life Sciences | Medicine and Health Sciences
In adipocytes that have been deprived of growth hormone (GH) for at least 3 hr, GH elicits a transient insulin-like response that is followed by a period of refractoriness to further insulin-like stimulation. Exposure of adipocytes to GH in the first hour of a 3-hr incubation prevents the appearance of insulin-like sensitivity. Intracellular Ca2+ concentration [( Ca2+]i) was measured in individual adipocytes that were loaded with fura-2 hexakis(acetoxymethyl) ester after preincubation in the presence (refractory) or absence (sensitive) of recombinant human GH at 100 ng/ml. Using a dual nitrogen laser imaging microscope with computer-assisted image processing to measure fluorescence changes, we observed that resting [Ca2+]i was 220 +/- 10 nM in refractory adipocytes and 110 +/- 6 nM in sensitive adipocytes (P less than 0.001). GH had no acute effect on [Ca2+]i in sensitive adipocytes but caused a sustained 3-fold increase in [Ca2+]i in refractory cells within 3 min (P less than 0.001). Insulin did not change [Ca2+]i in either sensitive or refractory adipocytes. In refractory cells treated with insulin and GH simultaneously, insulin completely blocked the rise in [Ca2+]i due to GH. Oxytocin elicited a prompt increase in [Ca2+]i followed by a quick return to resting levels in both sensitive and refractory cells. These findings indicate that basal [Ca2+]i is increased in refractory cells and that GH produces a sustained rise in [Ca2+]i only in refractory adipocytes. We suggest that the sustained increase in [Ca2+]i produced by GH in refractory cells prevents the expression of the insulin-like response.
Proc Natl Acad Sci U S A. 1991 Aug 1;88(15):6790-4.
Proceedings of the National Academy of Sciences of the United States of America
Schwartz Y, Goodman HM, Yamaguchi H. (1991). Refractoriness to growth hormone is associated with increased intracellular calcium in rat adipocytes. Open Access Publications by UMMS Authors. Retrieved from https://escholarship.umassmed.edu/oapubs/1826