Figure 8.

Scheme showing the proposed molecular mechanisms of the MLC1-induced Ca²⁺ regulation of VRAC. (1) Exposure to a hypotonic stress induces astrocyte (or astrocyte end-feet) swelling, which triggers the opening of TRPV4 and other Ca²⁺ channels (voltage-dependent and mechanosensitive Ca²⁺ channels). (2) The entry of extracellular Ca²⁺ promotes Ca²⁺ release from the ER, likely mediated by the InsP3 (or/and Ryanodine) receptors, through the CICR mechanism. (3) The consequent elevation of intracellular Ca²⁺ is sensed by the Ca²⁺-binding protein calmodulin (CaM), which binds and activates CaMKII. (4) By binding MLC1 and phosphorylating the threonine aa at position 17 (T17), CaMKII promotes MLC1 dimerization, stabilization, and functional activation. (5) Phosphorylated MLC1 potentiates TRPV4 [20] and VRAC channels, favoring ICl,_swell and regulatory volume decrease.