Palmitate and Beta Cell Insulin Secretion Figure 7. The repressive effects of palmitate on glucose-stimulated insulin secretion, PKB and ERK activation are not dependent upon fatty acid oxidation. (A) MIN6 b cells were incubated with varying concentrations of palmitate and 2-bromopalmitate (48 h) as indicated. Glucose (16 mM) was added for 1 h during serum starvation and the net change in glucose-stimulated insulin secretion assessed. (B) Cells were incubated in the absence or presence of 0.4 mM 2-bromopalmitate for 48 h and with glucose at the indicated concentration for 1 h. Cells were lysed and lysates immunoblotted for analysis of ERKThr202/Tyr204, PKBSer473, CaMKIIThr286 and total PKB, ERK and CaMKII. (C) Cells were incubated in the absence or presence of palmitate (0.4 mM) for 48 h and then after serum starvation cells were exposed to either L-carnitine (1 mM) or etomoxir (0.2 mM) for 2 h as indicated. Glucose (16 mM) was added during the final hour to induce GSIS and media removed for analysis of insulin content. Bars represent mean 6 SEM from 3 separate experiments and asterisks or a cross signify a significant difference from the untreated control values or between indicated bars (P,0.05). doi:10.1371/journal.pone.0025975.g007 activation of this kinase with a ‘‘knock-on’’ effect upon downstream targets involved in the insulin secretory process. Testing this latter possibility represents an important investigative goal of future work. In summary, whilst the lipotoxic effects of fatty acid over load will undoubtedly promote metabolic (endoplasmic reticulum and oxidative) stress and reduce the insulin secretion capacity of beta cells via activation of pro-apoptotic pathways [45], our studies indicate that insulin secretion from MIN6 b cells in response to glucose or amino acids is critically dependent upon the nutrient- induced activation of CaMKII and ERK. Sustained exposure of MIN6 b cells to palmitate results in impaired activation of both signalling molecules with an attendant reduction in insulin secretion. While there is no suggestion from our work that the PLoS ONE | www.plosone.org 9 October 2011 | Volume 6 | Issue 10 | e25975