Understanding the origin of and discovering a treatment for neurological complications in diabetes mellitus is one of the most important challenges facing both experimental investigation and clinical practice because of their severity and the large numbers of patients affected. Nevertheless, the mechanisms of the development of distal diabetic neuropathy, in particular the incidence of hyperalgesia and allodynia, pain syndromes or, the opposite, loss of sensitivity are not well understood. In particular, data about the changes of intracellular metabolism in nociceptive neurons under diabetic conditions are scarce, especially about changes in intracellular calcium signalling which could be quite important for Diabetologia (2001) 44: 1302±1309 Diabetes-induced changes in calcium homeostasis and the effects of calcium channel blockers in rat and mice nociceptive neurons

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Stimulation of T cell receptor in lymphocytes enhances Ca2؉ signaling and accelerates membrane trafficking. The relationships between these processes are not well understood. We employed membrane-impermeable lipid marker FM1-43 to explore membrane trafficking upon mobilization of intracellular Ca 2؉ in Jurkat T cells. We established that liberation of intracellular Ca 2؉ with T cell receptor agonist phytohemagglutinin P or with Ca 2؉ -mobilizing agents ionomycin or thapsigargin induced accumulation of FM1-43 within the lumen of the endoplasmic reticulum (ER), nuclear envelope (NE), and Golgi. FM1-43 loading into ER-NE and Golgi was not mediated via the cytosol because other organelles such as mitochondria and multivesicular bodies located in close proximity to the FM1-43-containing ER were free of dye. Intralumenal FM1-43 accumulation was observed even when Ca 2؉ signaling in the cytosol was abolished by the removal of extracellular Ca 2؉ . Our findings strongly suggest that release of intracellular Ca 2؉ may create continuity between the extracellular leaflet of the plasma membrane and the lumenal membrane leaflet of the ER by a mechanism that does not require global cytosolic Ca 2؉ elevation.Membrane trafficking plays an important role in shaping T cell responses. For example, it is well established that engagement of TCR 1 with an antigen triggers fast trafficking of the receptor between the PM and endocytic organelles, resulting in serial TCR engagements and an amplification of intracellular signaling (1). TCR stimulation is followed by a fast liberation of Ca 2ϩ from Ca 2ϩ -storing organelles, such as ER and Golgi (2, 3). Alteration of Ca 2ϩ homeostasis induces a variety of cellular responses ranging from changes in cell shape and motility to activation of transcription factors (2). However, it is not clear whether changes in intracellular Ca 2ϩ dynamics affect membrane trafficking in T lymphocytes.Styryl dye FM1-43 is a fluorescent membrane marker that reversibly partitions into but does not penetrate biological membranes (4). We have shown previously that FM1-43 was readily internalized from the PM into the endocytic compartments of human T cells by constitutive endocytosis (5). We also demonstrated that Ca 2ϩ ionophore ionomycin (Iono) or thapsigargin (Tg), a sarco-endoplasmic reticulum calcium ATPase pumps blocker, facilitated FM1-43 internalization (5). These findings suggested that elevation of cytosolic Ca 2ϩ concentration ([Ca 2ϩ ] i ) might accelerate the rate of endocytosis in T cells. However, an EM study performed previously in the Xenopus larvae hair cells revealed the presence of FM1-43 within nonendocytic organelles such as ER, NE, and mitochondria (6). These results led to a suggestion that FM1-43 can penetrate the PM and diffuse through the cytosol. To further investigate the nature of enhanced FM1-43 internalization following liberation of intracellular Ca 2ϩ in T cells, we studied subcellular distribution of FM1-43 using correlative fluorescence and electron microscopy.We found that sti...