Damage to the sarcoplasmic reticulum by venom of the Mexican black-tailed rattlesnake ( <i>Crotalus molossus nigrescens</i> ): inhibition of the Ca ²⁺ -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 <i>in vitro</i> toxic effect of crotalid venom on the enzymatic activity of SERCA, using venom of the Mexican black-tailed rattlesnake, <i>Crotalus molossus nigrescens</i>, (v<i>Cmn</i>), and SERCA-enriched sarcoplasmic reticulum (SR) microsomes from rabbit skeletal muscle as experimental models. Enzymatic assays revealed significant v<i>Cmn</i>-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 v<i>Cmn</i> 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 v<i>Cmn</i>-induced myotoxicity.