ABNORMALITIES IN THE REGULATION OF BLOOD-PLATELET FREE CYTOSOLIC CALCIUM IN MALIGNANT HYPERTHERMIA .2. PIG PLATELETS

Since 1966 the domestic pig has served as the animal model in Malignan t Hyperthermia (MH) research [1]. The use of genetically well-defined pigs rendered it possible to test the method for diagnosing MH-suscept ibility of patients presented in the preceding paper. Thus, the effect of halothane on intracellular calcium movements was studied in Quin-2 - and chlorotetracycline-loaded pig platelets. In 'Ca2+-free' suspensi ons the resting level of free cytosolic Ca2+ was about 60 nM. In contr ast to the results with human platelets there were no significant diff erences between pig genotypes either in the absence or in the presence of external calcium. After addition of halothane, a mobilization of i ntracellular membrane-bound calcium can be observed. However, the calc ium mobilization is not accompanied by a marked increase in fluorescen ce intensity of Quin-2-loaded platelets. Thus, in the absence of exter nal calcium, halothane produces only a slight increase in free cytosol ic Ca2+. Nevertheless, the calcium rises measured in platelets from af fected animals were statistically significantly higher than those from normal subjects. However, in the presence of 1 mM external calcium, a rapid increase in free cytosolic calcium can be detected after haloth ane addition. This suggests that halothane causes a marked, dose-depen dent increase in Ca2+ permeability of the plasma membrane. Compared to the control group, significantly enhanced calcium permeability was fo und, not only in homozygous positive pigs, but also in heterozygous an imals.