Patients with malignant hyperthermia demonstrate an altered calcium control mechanism in B lymphocytes.
BACKGROUND
Altered Ca2+ homeostasis in skeletal muscle is a key molecular event triggering malignant hyperthermia (MH) in malignant hyperthermia-susceptible (MHS) individuals. Genetic studies have shown that mutations in the type 1 ryanodine receptor (RYR1) are associated with MH susceptibility. Because human B lymphocytes express the RYR1, it is hypothesized that Ca2+ homeostasis in B lymphocytes is altered in MHS individuals.


METHODS
This study investigated the Ca2+ response of B cells to caffeine and 4-chloro-m-cresol in 13 MHS and 21 MH-negative (MHN) individuals who had been diagnosed by caffeine halothane contracture test (CHCT) and 18 healthy volunteers. Changes in [Ca2+]i in B cells were measured directly in fluo-3 loaded cells using a dual-color flow cytometric technique. Further, B cell phenotype was correlated with CHCT results in a family with the Val2168Met (G6502A) mutation.


RESULTS
Caffeine-induced (50 mm) increases in [Ca2+]i in B cells were significantly greater in MHS than in MHN (P = 0.0004), control (P = 0.0001) or non-MHS (MHN and control) individuals (P < 0.0001). The 4-chloro-m-cresol-induced (400 microm) increases in [Ca2+]i were also significantly different between MHS and controls (P = 0.003) or between MHS and non-MHS (MHN and control) individuals (P = 0.0078). A study of a family with the Val2168Met mutation demonstrated expression of the RYR1 mRNA mutant in B cells from the family members with MHS phenotype and a clear segregation of genotype with B-cell phenotype.


CONCLUSIONS
The Ca2+ responses to caffeine or 4-chloro-m-cresol in B lymphocytes showed significant differences between MHS and MHN (or control) individuals. Although the molecular mechanisms of these alterations are currently undetermined, the results suggest that the enhanced Ca2+ responses are associated with mutations in the RYR1 gene in some MHS individuals.
Sei
Yoshitatsu
Y
Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA. ysei@usuhs.mil
Brandom
Barbara W
BW
Bina
Saiid
S
Hosoi
Eiji
E
Gallagher
Kathleen L
KL
Wyre
Hadley W
HW
Pudimat
Paul A
PA
Holman
Steve J
SJ
Venzon
David J
DJ
Daly
John W
JW
Muldoon
Sheila
S
D000293:Adolescent; D000328:Adult; D001402:B-Lymphocytes / Q000378:metabolism*; D002110:Caffeine; D002118:Calcium / Q000378:metabolism*; D002648:Child; D003408:Cresols; D004198:Disease Susceptibility; D006221:Halothane; D006801:Humans; D008305:Malignant Hyperthermia / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism*; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009154:Mutation; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics
D003408:Cresols; D019837:Ryanodine Receptor Calcium Release Channel; C006984:chlorocresol; D002110:Caffeine; D002118:Calcium; D006221:Halothane