SERUM FROM DIABETIC BB W RATS ENHANCES CALCIUM CURRENTS IN PRIMARY SENSORY NEURONS/

We examined the hypothesis that exposure of nondiabetic rat dorsal roo t ganglion (DRG) neurons to sera from diabetic BB/W rats would produce an increase in calcium currents associated with impaired regulation o f the inhibitory G protein-calcium channel complex. Acutely dissociate d rat DRGs were incubated for 18-24 h in medium supplemented with sera (10% vol/vol) from either diabetic rats with neuropathy or age-matche d, nondiabetic controls. Exposure of DRG neurons to sera from diabetic BB/W rats resulted in a surface membrane immunofluorescence pattern w hen treated with an anti-rat light-chain antibody that was not observe d in neurons exposed to control sera. Calcium current density (I-DCa) was assessed with the use of the whole cell variation of the patch-cla mp technique. I-DCa in neurons exposed to diabetic sera was significan tly increased compared with neurons exposed to control sera. Guanine n ucleotide-binding (G) protein regulation of calcium channel function w as examined with the use of a two-pulse ''facilitation'' or I-DCa enha ncement protocol in the presence of activators [guanosine 5'-O-(3-thio triphosphate) (GTP gamma S)] or antagonists [guanosine 5'-O-( 2-thiodi phosphate) (GDP beta S) and pertussis toxin (PTX)] of G protein functi on. Facilitation was significantly decreased in neurons exposed to dia betic sera. Intracellular diffusion of neurons with CDP beta s blocked facilitation, whereas dialysis with GTP gamma s increased facilitatio n to a similar magnitude in neurons exposed to either diabetic or cont rol sera. Treatment with PTX resulted in a significant increase in I-D Ca and similar to 50% decrease in facilitation in neurons treated with control sera but no significant changes in neurons exposed to diabeti c 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 ca lcium influx. Regulation of the inhibitory G protein-calcium channel c omplex involves PTX-sensitive and -insensitive G proteins.