CHONDROITIN SULFATE PROTEOGLYCAN ELEVATES CYTOPLASMIC CALCIUM IN DRG NEURONS

Proteoglycans have been implicated in neuronal path-finding during dev elopment, yet related second messenger and signaling systems are unkno wn. We have used the calcium indicator fura-2/AM to monitor cytoplasmi c calcium ion concentration ([Ca2+](i)) in chick dorsal root ganglion (DRG) neuronal growth cones elongating on laminin during contact with chondroitin sulfate proteoglycan (CSPG): (1) to determine whether ther e is a change in [Ca2+](i) in neurons that contact CSPG, and (2) to de termine whether changes in [Ca2+](i) are necessary for inhibition of g rowth cone migration. The majority of DRG neurons responded to CSPG co ntact with a transient rise in [Ca2+](i) (mean Delta[Ca2+](i) above re sting level was 554 +/- 109 nM; P < 0.0001). The effect of CSPG contac t was concentration dependent and required the carbohydrate moiety of CSPG. Addition of soluble CSPG did not elevate [Ca2+]. Treatment with reagents that blocked plasma membrane calcium channels, or that pertur bed intracellular Ca2+ stores, indicated that extracellular Ca2+ was t he major source of the [Ca2+](i) elevation, and that Ca2+ entry occurr ed through non-voltage-gated calcium channels. Although general Ca2+ c hannel blockers abolished the CSPG-induced [Ca2+](i) rise, they did no t abolish growth cone avoidance of surface-bound CSPG in these assays. We conclude: (1) that DRG neurons elevate [Ca2+](i) in response to CS PG contact to levels that can modify cytoskeletal mechanisms of growth cone migration, and (2) that avoidance of substratum-bound CSPG may n ot be dependent upon elevated [Ca2+](i). (C) 1994 Academic Press, Inc.