Effect of Different Formulations of Magnesium Chloride Used As Anesthetic Agents on the Performance of the Isolated Heart of .

Magnesium chloride (MgCl) is commonly used as a general anesthetic in cephalopods, but its physiological effects including those at cardiac level are not well-characterized. We used an isolated perfused systemic heart preparation from the common octopus, , to investigate: (a) if exposure to MgCl formulations had an effect on cardiac function and, if so, could this impact recovery and (b) direct effects of MgCl formulations on cardiac function. hearts removed from animals exposed to 3.5% MgCl in sea water (20 min) or to a mixture of MgCl+ ethanol (1.12/1%; 20 min) showed cardiac function (heart rate, stroke volume, cardiac output) comparable to hearts removed from animals killed under hypothermia. However, 3.5% MgCl (1:1, sea water: distilled water, 20 min) produced a significant impairment of the Frank-Starling response as did 45 min exposure to the MgCl+ ethanol mixture. Perfusion of the isolated heart with MgCl± ethanol formulations produced a concentration-related bradycardia (and arrest), a decreased stroke volume and cardiac output indicating a direct effect on the heart. The cardiac effects of MgCl are discussed in relation to the involvement of magnesium, sodium, chloride, and calcium ions, exposure time and osmolality of the formulations and the implications for the use of various formulations of MgCl as anesthetics in octopus. Overall, provided that the exposure to 3.5% MgCl in sea water or to a mixture of MgCl+ ethanol is limited to ~20 min, residual effects on cardiac function are unlikely to impact post-anesthetic recovery.