HEPARIN FORMULAS CONTAINING CHLOROCRESOL INDUCE CONTRACTURES IN MALIGNANT HYPERTHERMIA SUSCEPTIBLE SKELETAL MUSCLE IN VITRO

Abstract

S313 The preservative 4-chloro-m-cresol (4CmC) is a potent and highly specific activator of ryanodine receptor-mediated Ca2+ release [1] and induces contractures in [micro sign]molar ranges in skeletal muscles of Malignant Hyperthermia susceptible (MHS) patients. [2] Clinical formulas for heparin contain 4CmC in a reasonable amount. We studied whether these heparin formulas induce contractures in isolated MHS human skeletal muscles and whether significant serum levels of 4CmC are reached after heparinization in cardiopulmonary bypass patients. METHODS: Muscle biopsy and in vitro contracture test were performed acc. to the European protocol. [3] With informed consent surplus muscle strips of MHS and normal (MHN) patients were exposed in the same experimental setting to clinical formulas of heparin, i.e. Thrombophob[registered sign] (1mg/ml 4CmC) and Liquemin[registered sign] (0.8mg/ml 4CmC), and to 4CmC (1mg/ml) and preservative-free heparin in increasing concentrations resp.. The effects on muscle contractures were compared between MHS and MHN. In a second step, serum levels of 4CmC in cardiopulmonary bypass patients were measured after heparinization (500U/kg) by HPLC at 5, 10 and 60 min. Statistical analysis was performed by U-test (p < 0.05). RESULTS: 7 MHN/3 MHS muscle strips were incubated with Thrombophob[registered sign], 9 MHN/6 MHS with Liquemin[registered sign], 6 MHN/7 MHS with 4CmC, and 10 MHN/6 MHS with heparin. Clinical formulas of heparin as well as 4CmC induced significant higher contractures in MHS than MHN bundles. Preservative-free heparin caused no contractures. In 13 cardiopulmonary bypass patients, no significant serum levels of 4CmC could be detected with a detection threshold of 4[micro sign]M 4CmC. CONCLUSION: Heparin formulas, containing 4CmC, induce dose dependent contractures in vitro in MHS human skeletal muscle at about 60 [micro sign]M 4CmC. However in vivo, 4CmC serum concentrations with therapeutic heparinization are at least 1/15 lower. The lipophilicity of 4CmC with a high volume of distribution may account for this findings. MHS patients seem to be not at risk by clinical heparin formulas, containing chlorocresol.