P2X4 receptors in activated C8-B4 cells of cerebellar microglial origin.
We investigated the properties and regulation of P2X receptors in immortalized C8-B4 cells of cerebellar microglial origin. Resting C8-B4 cells expressed virtually no functional P2X receptors, but largely increased functional expression of P2X4 receptors within 2-6 h of entering the activated state. Using real-time polymerase chain reaction, we found that P2X4 transcripts were increased during the activated state by 2.4-fold, but this increase was not reflected by a parallel increase in total P2X4 proteins. In resting C8-B4 cells, P2X4 subunits were mainly localized within intracellular compartments, including lysosomes. We found that cell surface P2X4 receptor levels increased by approximately 3.5-fold during the activated state. This change was accompanied by a decrease in the lysosomal pool of P2X4 proteins. We next exploited our findings with C8-B4 cells to investigate the mechanism by which antidepressants reduce P2X4 responses. We found little evidence to suggest that several antidepressants were antagonists of P2X4 receptors in C8-B4 cells. However, we found that moderate concentrations of the same antidepressants reduced P2X4 responses in activated microglia by affecting lysosomal function, which indirectly reduced cell surface P2X4 levels. In summary, our data suggest that activated C8-B4 cells express P2X4 receptors when the membrane insertion of these proteins by lysosomal secretion exceeds their removal, and that antidepressants indirectly reduce P2X4 responses by interfering with lysosomal trafficking.
Toulme
Estelle
E
Department of Physiology, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
Garcia
Angie
A
Samways
Damien
D
Egan
Terrance M
TM
Carson
Monica J
MJ
Khakh
Baljit S
BS
D000818:Animals; D000928:Antidepressive Agents / Q000008:administration & dosage*; D002460:Cell Line; D002531:Cerebellum / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D018048:Receptors, Purinergic P2 / Q000187:drug effects / Q000378:metabolism*; D058848:Receptors, Purinergic P2X4
D000928:Antidepressive Agents; C548227:P2rx4 protein, mouse; D018048:Receptors, Purinergic P2; D058848:Receptors, Purinergic P2X4