Context and objectives: The present study was designed to investigate whether 3,4-methylenedioxymethamphetamine (MDMA, 'Ecstasy') increases the sensitivity of the contractile apparatus to calcium in muscle fibres from malignant hyperthermia-susceptible and malignant hyperthermia-negative pigs, whether it causes calcium ion release from the sarcoplasmic reticulum and whether it inhibits calcium reuptake into the sarcoplasmic reticulum.
Design: Experimental study, using a model of porcine saponin-skinned fibres.
Results: Administration of MDMA in concentrations of 1, 2 and 4 mmol l(-1)l did not result in relevant force transients in skinned muscle fibres of malignant hyperthermia-susceptible or malignant hyperthermia-negative pigs. Furthermore, MDMA in these concentrations did not alter calcium ion loading of the sarcoplasmic reticulum in either group. With regard to changes in the calcium ion sensitivity of the contractile proteins, however, MDMA dose-dependently increased (pCa50) values (negative decadic logarithm of [Ca2+] at which isometric force is half-maximal) in both groups.
Conclusion: In the present study, we were able to demonstrate that MDMA dose-dependently increases the sensitivity of the contractile apparatus to calcium in both malignant hyperthermia-susceptible and malignant hyperthermia-negative fibres. Consequently, the malignant hyperthermia status should not affect the calcium sensitivity of the contractile apparatus. However, the increased calcium sensitivity is an important finding that must be appreciated, particularly in relation to the agonistic effect of MDMA at the nicotinic acetylcholine receptor, which increases intracellular calcium ion concentrations.