Capacitative Ca2+ influx in glial cells is inhibited by glycolytic inhibitors

In non-excitable cells, stimulation of phosphoinositide (PI) turnover and inhibition of the endoplasmic reticulum (ER) Ca²⁺-ATPase are methods commonly used to deplete calcium stores, resulting in a capacitative Ca²⁺ influx (i.e., Ca²⁺ release-activated Ca²⁺ influx). Since this Ca²⁺ influx in glial cells has not been thoroughly investigated, we have used C₆ glioma cells as a glial cell model to study this phenomenon. On adding cyclopiazonic acid (CPA) or thapsigargin (TG) (two ER Ca²⁺-ATPase inhibitors) in Ca²⁺-free medium, only a small transient increase in intracellular Ca²⁺ was seen. After depletion of the stored Ca²⁺, a marked Ca²⁺ influx, followed by a prolonged plateau, was seen on re-addition of extracellular Ca²⁺ ions (2 mM), i.e., capacitative Ca²⁺ influx. A similar effect was seen on adding ATP, known to deplete the inositol triphosphate (IP₃)-sensitive Ca²⁺ store in C₆ cells. After various degrees of store depletion, the amplitude of the capacitative Ca²⁺ influx was found to be highly dependent on the amount of Ca²⁺ remaining in the store. This Ca²⁺ influx was markedly inhibited by (1) La³⁺ and Ni²⁺, (2) SK&F 96365, econazole, and miconazole, and (3) membrane depolarization, clearly showing that this Ca²⁺ influx after store depletion in C₆ cells is a capacitative mechanism. Interestingly, the capacitative Ca²⁺ influx can be inhibited by a reduction in intracellular ATP (ATP_i) levels in glial cells. The role of ATP_i in the capacitative Ca²⁺ influx is discussed. GLIA 21:315–326, 1997. © 1997 Wiley-Liss, Inc.