Serum From Diabetic BB/W Rats Enhances Calcium Currents in Primary Sensory Neurons

Abstract

We examined the hypothesis that exposure of nondiabetic rat dorsal root ganglion (DRG) neurons to sera from diabetic BB/W rats would produce an increase in calcium currents associated with impaired regulation of the inhibitory G protein-calcium channel complex. Acutely dissociated rat DRGs were incubated for 18-24 h in medium supplemented with sera (10% vol/vol) from either diabetic rats with neuropathy or age-matched, nondiabetic controls. Exposure of DRG neurons to sera from diabetic BB/W rats resulted in a surface membrane immunofluorescence pattern when treated with an anti-rat light-chain antibody that was not observed in neurons exposed to control sera. Calcium current density (IDCa) was assessed with the use of the whole cell variation of the patch-clamp technique. IDCa in neurons exposed to diabetic sera was significantly increased compared with neurons exposed to control sera. Guanine nucleotide-binding (G) protein regulation of calcium channel function was examined with the use of a two-pulse "facilitation" or IDCa enhancement protocol in the presence of activators [guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)] or antagonists [guanosine 5'-O-(2-thiodiphosphate) (GDP beta S) and pertussis toxin (PTX)] of G protein function. Facilitation was significantly decreased in neurons exposed to diabetic sera. Intracellular diffusion of neurons with GDP beta s blocked facilitation, whereas dialysis with GTP gamma s increased facilitation to a similar magnitude in neurons exposed to either diabetic or control sera. Treatment with PTX resulted in a significant increase in IDCa and approximately 50% decrease in facilitation in neurons treated with control sera but no significant changes in neurons exposed to diabetic sera. We conclude that serum from diabetic BB/W rats with neuropathy contains an autoimmune immunoglobulin that impairs regulation of the inhibitory G protein-calcium channel complex, resulting in enhanced calcium influx. Regulation of the inhibitory G protein-calcium channel complex involves PTX-sensitive and -insensitive G proteins.

CaV1.2 and CaV1.3 channel hyperactivation in mouse islet β cells exposed to type 1 diabetic serum

“…and Ca V 1.3 -/-b cells. This is in line with previous findings from our group and others [19,[42][43][44][45]. More importantly, we are able to mechanistically interpret T1D serum-induced hyperactivation of b cell Ca V 1 channels by thoroughly examining the biophysical properties of single Ca V 1 channels in Ca V 1.…”

Sera from patients with type 2 Diabetes and Neuropathy Induce Autophagy and Colocalization with Mitochondria in SY5Y cells

“…The experiments showing increased labeling of autophagosomes with anti-LC3 immunoreactivity in DRG neurons of streptozotocindiabetic rats follow our earlier observations highlighting a potential role for autoimmunity in the induction of cellular stress 6 and apoptosis in diabetic neuropathy. 5 Those observations are extended in the present report by the experiments conducted with SH-SY5Y cells, exposed to normal or diabetic neuropathic sera, in media containing similar concentrations of glucose and other nutrients.…”

“…1 In addition to metabolic and endocrine abnormalities, recent studies support the presence of autoimmune immunoglobulin in the sera of patients with type 1 and type 2 diabetes that induce apoptosis in cultured neurons. [2][3][4] These autoimmune antibodies are present in complement-inactivated sera from humans 5 and rat models 6 and suggest a role for autoantibodies in the pathophysiology of diabetic neuropathy. It is noteworthy that the level of apoptosis observed in primary afferent nerves in situ (~1-4%) is consistent with the modest loss in neurons reported in peripheral nerve tissues in diabetes, [7][8][9] making it difficult to account for the more robust deficits in peripheral nerve function, e.g., slowing in nerve conduction velocity, altered sensation and autonomic nervous system dysfunction observed concurrently with apoptosis.…”

“…Our previous studies with this model have shown that after 4-8 weeks of diabetes the rats exhibit a variety of functional derangements, similar to those observed in human patients with diabetic neuropathy including slowing of nerve conduction velocity, increased calcium influx, impaired inhibitory G-protein function, impaired mitochondrial function and activation of the apoptosis cascade in acutely dissociated DRG neurons. [5][6][7][8] Animals were narcotized through carbon dioxide inhalation and immediately perfused with 4% buffered paraformaldehyde for 20 min via a cardiac catheter. Lower thoracic and lumbar DRGs, were subsequently removed and processed for immunohistochemistry.…”

Cell-Specific Alterations of T-Type Calcium Current in Painful Diabetic Neuropathy Enhance Excitability of Sensory Neurons

“…These rats, after 8 months of diabetes, also upregulate T-type channels in small DRG cells (Hall et al, 1995). Serum from BB/W rats increases both HVA and T-type currents in DRG cells grown in culture without alterations in T-type channel inactivation kinetics (Ristic et al, 1998). In contrast, we found that T-type channels in medium-size neurons in STZ-induced diabetic neuropathy show prominent changes in voltage-dependent inactivation, allowing a greater fraction of the channels to be available for activation during both short and prolonged periods of depolarization.…”