Manganese inhibits ATP-induced calcium entry through the transient receptor potential channel TRPC3 in astrocytes

Chronic exposure to elevated levels of manganese (Mn2+) causes neuronal injury and inflammatory activation of glia. Astrocytes selectively accumulate Mn2+, which inhibits mitochondrial respiration and increases production of reactive oxygen species. We previously reported that sub-acute exposure to low micromolar levels of Mn2+ in primary astrocytes inhibited ATP-induced calcium (Ca2+) signaling, associated with decreased levels of endoplasmic reticulum Ca2+ and increased mitochondrial Ca2+ loads. In the present studies, we postulated that the mechanism underlying the capacity of Mn2+ to inhibit these purinergic signals in astrocytes could be due to competition with Ca2+ for entry through a plasma membrane channel. These data demonstrate that acutely applied Mn2+ rapidly inhibited ATP-induced Ca2+ waves and transients in primary striatal astrocytes. Mn2+ also decreased influx of extracellular Ca2+ induced by 1-oleoyl-2-acetyl-sn-glycerol (OAG), a direct activator of the transient receptor potential channel, TRPC3. The TRPC3 inhibitor, pyrazole-3, prevented ATP- and OAG-dependent transport of Mn2+ from extracellular stores, demonstrated by a dramatic reduction in the rate of fluorescence quenching of Fura-2. These data indicate that Mn2+ can acutely inhibit ATP-dependent Ca2+ signaling in astrocytes by blocking Ca2+ entry through the receptor-operated cation channel, TRPC3. Loss of normal astrocytic responses to purinergic signals due to accumulation of Mn2+ could therefore comprise critical homeostatic functions necessary for metabolic and trophic support of neurons.

► Manganese rapidly inhibits calcium waves in astrocytes. ► ATP- and OAG-induced calcium transients are suppressed by manganese. ► The TRPC3 inhibitor pyrazole-3 prevents manganese entry in astrocytes.