Abnormal rapid Ca2+ release from sarcoplasmic reticulum of malignant hyperthermia susceptible pigs.
Using the rapid filtration technique to investigate Ca2+ movements across the sarcoplasmic reticulum (SR) membrane, we compare the initial phases of Ca2+ release and Ca2+ uptake in malignant hyperthermia susceptible (MHS) and normal (N) pig SR vesicles. Ca2+ release is measured from passively loaded SR vesicles. MHS SR vesicles present a 2-fold increase in the initial rate of calcium release induced by 0.3 microM Ca2+ (20.1 +/- 2.1 vs. 6.3 +/- 2.6 nmol mg-1 s-1). Maximal Ca2+ release is obtained with 3 microM Ca2+. At this optimal concentration, rate of Ca2+ efflux in absence of ATP is 55 and 25 nmol mg-1 s-1 for MHS and N SR, respectively. Ca(2+)-induced Ca2+ release is inhibited by Mg2+ in a dose-dependent manner for both MHS and N pig SR vesicles (K1/2 = 0.2 mM). Caffeine (5 mM) and halothane (0.01% v/v) increase the Ca2+ sensitivity of Ca(2+)-induced Ca2+ release. ATP (5 mM) strongly enhances the rate of Ca2+ efflux (to about 20-40-fold in both MHS and N pig SR vesicles). Furthermore, both types of vesicles do not differ in their high-affinity site for ryanodine (Kd = 12 nM and Bmax = 6 pmol/mg), lipid content, ATPase activity and initial rate of Ca2+ uptake (0.948 +/- 0.034 vs. 0.835 +/- 0.130 mumol mg-1 min-1 for MHS and N SR, respectively). Our results show that MH syndrome is associated to a higher rate of Ca2+ release in the earliest phase of the calcium efflux.
Carrier
L
L
Laboratoire de Biophysique Moléculaire et Cellulaire, LBIO/CENG, Grenoble, France.
Villaz
M
M
Dupont
Y
Y
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D005374:Filtration; D006221:Halothane / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008305:Malignant Hyperthermia / Q000378:metabolism*; D012433:Ryanodine / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D013552:Swine
D015220:Calcium Channels; D012433:Ryanodine; D002110:Caffeine; D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium; D006221:Halothane