Coelenterazine h (2-Deoxycoelenterazine, CLZN-h) is a luminophore derivative of coelenterazine, serves as a luminescent substrate for RLuc8. It enhances the sensitivity of recombinant aequorin to Ca²⁺, enabling the detection of subtle calcium changes in response to touch and wounding and making it a valuable tool for measuring small Ca²⁺ fluctuations.