Damage to the sarcoplasmic reticulum by venom of the Mexican black-tailed rattlesnake (Crotalus molossus nigrescens): inhibition of the Ca2+-ATPase and membrane lipid disruption.

Snakebite envenomation is a public health problem in many areas in the world and is a significant cause of disability and death. Crotalid venoms consist of a cocktail of peptides and enzymes that can cause myonecrotoxic lesions, which are associated with irreversible loss of muscle tissue. The sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) is a transmembrane protein with a critical role in maintaining cellular Ca²⁺ homeostasis, which is central in facilitating skeletal and cardiac muscle contraction/relaxation. Crotalid venom-induced myotoxicity has been linked to alterations in the intracellular levels of Ca²⁺. However, the specific mechanisms, including SERCA's involvement, are poorly understood. Thus, we investigated the in vitro toxic effect of crotalid venom on the enzymatic activity of SERCA, using venom of the Mexican black-tailed rattlesnake, Crotalus molossus nigrescens, (vCmn), and SERCA-enriched sarcoplasmic reticulum (SR) microsomes from rabbit skeletal muscle as experimental models. Enzymatic assays revealed significant vCmn-induced decreases in SERCA activity in a time- and dose-dependent manner. Thin layer chromatography and phospholipid hydrolysis measurements showed significant SR membrane damage. The results suggest that vCmn affects SERCA functionality and compromises the integrity of the SR membrane, both of which are critical for skeletal muscle function and could thus be key mediators of vCmn-induced myotoxicity.