Shi, Hang, Yuan-Di Halvorsen, Pamela N. Ellis, William O. Wilkison, and Michael B. Zemel. Role of intracellular calcium in human adipocyte differentiation. Physiol Genomics 3: 75–82, 2000.—Intracellular calcium ([Ca²⁺]_i) modulates adipocyte lipid metabolism and inhibits the early stages of murine adipogenesis. Consequently, we evaluated effects of increasing [Ca²⁺]_i in early and late stages of human adipocyte differentiation. Increasing [Ca²⁺]_i with either thapsigargin or A23187 at 0–1 h of differentiation markedly suppressed differentiation, with a 40–70% decrease in triglyceride accumulation and glycerol-3 phosphate dehydrogenase (GPDH) activity (P < 0.005). However, a 1-h pulse of either agent at 47–48 h only modestly inhibited differentiation. Sustained, mild stimulation of Ca²⁺ influx with either agouti protein or 10 mM KCl-induced depolarization during 0–48 h of differentiation inhibited triglyceride accumulation and GPDH activity by 20–70% (P < 0.05) and markedly suppressed peroxisome proliferator-activated receptor gamma (PPARγ) expression. These effects were reversed by Ca²⁺ channel antagonism. In contrast, Ca²⁺ pulses late in differentiation (71–72 h or 48–72 h) markedly increased these markers of differentiation. Thus increasing [Ca²⁺]_i appears to exert a biphasic regulatory role in human adipocyte differentiation, inhibiting the early stages while promoting the late stage of differentiation and lipid filling.