Related Experiment Videos
Down-regulation of cell surface insulin receptors in primary cultured rat adipocytes by sodium vanadate
Abstract:
Sodium vanadate, a potent phosphotyrosine phosphatase inhibitor, was found to down-regulate the number of cell surface receptors in primary cultured adipocytes (50% receptor loss by 24 h; 65% loss by 48 h; ED50, 17 and 9 microM, respectively). The characteristics of vanadate-induced down-regulation were distinguished by three salient features. First, time-course studies revealed a lag period of 4-6 h preceding vanadate-induced receptor loss. This lag period was not due to slow diffusion of vanadate into the cell, since it could not be shortened using a very high dose of vanadate (1 mM). Second, vanadate was found to trigger receptor loss, such that down-regulation continued after vanadate removal. Thus, no immediate down-regulation was observed in adipocytes exposed to 80 microM vanadate for 6 h. However, when cells were washed and reincubated in vanadate-free medium for an additional 18 h (24 h total), a 50% receptor loss was seen. Lastly, we found that vanadate-induced down-regulation was not readily reversible, since receptor recovery was not observed when 24-h down-regulated cells were reincubated in vanadate-free medium for an additional 24 h. These three features of vanadate-induced receptor loss are remarkably similar to the characteristics of insulin-induced down-regulation. In studies examining the relationship between protein synthesis and vanadate-induced down-regulation, we found that vanadate markedly stimulated the overall rate of protein synthesis in 24-h treated adipocytes (a 42% increase; ED50, 3 microM), and that cycloheximide treatment markedly blunted vanadate-induced loss of cell surface receptors. Overall, these studies are consistent with the hypothesis that tyrosine phosphorylation plays a role in regulating the number of cell surface insulin receptors.
Insights
Sodium vanadate, a phosphatase inhibitor, reduces cell surface receptors in adipocytes. This process, similar to insulin effects, involves protein synthesis and is not immediately reversible.
Area of Science:
- Biochemistry
- Cell Biology
- Endocrinology
Background:
- Sodium vanadate is a known phosphotyrosine phosphatase inhibitor.
- Cell surface receptors play crucial roles in cellular communication and function.
- Insulin receptor regulation is vital for glucose homeostasis.
Purpose of the Study:
- To investigate the effects of sodium vanadate on cell surface receptor regulation in primary cultured adipocytes.
- To characterize the mechanism and features of vanadate-induced receptor down-regulation.
- To explore the relationship between protein synthesis and vanadate-induced receptor loss.
Main Methods:
- Primary cultured adipocytes were treated with varying concentrations of sodium vanadate.
- Time-course studies were conducted to observe receptor loss over 24-48 hours.
- Experiments involved vanadate removal, cycloheximide treatment, and protein synthesis rate measurements.
Main Results:
- Sodium vanadate significantly down-regulated cell surface receptors in adipocytes, with 50% loss by 24h and 65% by 48h.
- Vanadate-induced down-regulation exhibited a 4-6h lag period, continued after vanadate removal, and was not readily reversible.
- Vanadate stimulated protein synthesis and cycloheximide blunted receptor loss, suggesting a role for protein synthesis.
Conclusions:
- Vanadate-induced receptor down-regulation in adipocytes shares characteristics with insulin-induced down-regulation.
- Tyrosine phosphorylation is implicated in the regulation of cell surface insulin receptor numbers.
- These findings contribute to understanding receptor regulation mechanisms in adipocytes.