Comparison of European and North American Malignant Hyperthermia Diagnostic Protocol Outcomes for Use in Genetic Studies

Background Halothane and caffeine diagnostic protocols and an experimental ryanodine test from the North American Malignant Hyperthermia (MH) Group (NAMHG) and the European MH Group (EMHG) have not been compared in the same persons until now. Methods The outcomes of the NAMHG and EMHG halothane and caffeine contracture tests were compared in 84 persons referred for diagnostic testing. In addition, the authors assessed the experimental ryanodine protocol in 50 of these persons. Results Although the NAMHG and EMHG halothane protocols are slightly different methodologically, each yielded outcomes in close (84-100%) agreement with diagnoses made by the other protocol. Excluding 23 persons judged to be equivocal (marginally positive responders) by the EMHG protocol resulted in fewer persons classified as normal and MH susceptible (42 and 19, respectively) than those classified by the NAMHG protocol (48 and 34, respectively). For the 61 persons not excluded as equivocal, the diagnoses were identical by both protocols, with the exception of one person who was diagnosed as MH susceptible by the NAMHG protocol and as "normal" by the EMHG protocol. The NAMHG protocol produced only two equivocal diagnoses. Therefore, a normal or MH diagnosis by the NAMHG protocol was frequently associated with an equivocal diagnosis by the EMHG protocol. The time to 0.2-g contracture after the addition of 1 microM ryanodine completely separated populations, which was in agreement with the EMHG protocol and, except for one person, with the NAMHG protocol. Conclusions Overall, the NAMHG and EMHG protocols and the experimental ryanodine test yielded similar diagnoses. The EMHG protocol reduced the number of marginal responders in the final analysis, which may make the remaining diagnoses slightly more accurate for use in genetic studies.

BAY K 8644 and ClO4- potentiate caffeine contracture without Ca2+ release channel activation

Effects of perchlorate (ClO4-) and BAY K 8644 on caffeine contracture and Ca2+ release channel current were studied in frog skeletal muscle. Single fibers produced a small transient contracture on addition of 2.2 mM caffeine. ClO4 at 10 mM enhanced caffeine contracture 3.7-fold. This effect was inhibited by 10 microM nifedipine pretreatment. An increase in caffeine contracture was also obtained after exposure to 0.1 microM BAY K 8644 for 1 h. At 20 mM, external K+ potentiated caffeine contracture 2.2-fold. ClO4- (< 10 mM) and BAY K 8644 (0.1-1 microM) did not affect open probability (Po), unitary conductance, and open and closed time constants of the Ca2+ release channel current. BAY K 8644 at 0.1 microM did not further enhance the channel that had been activated by 2 mM caffeine. However, 20-30 mM ClO4 increased Po significantly and led the channel to a long open state by increasing the slow open time constant and decreasing the fast closed time constant. These results suggest that binding of ClO4 and BAY K 8644 to dihydropyridine receptors elicits a further increase in Ca2+ release from the sarcoplasmic reticulum.

Rapid cooling contractures in rat skinned myocardium: effects of isoflurane and halothane

Rapid cooling contractures (RCCs) have been elicited in rat ventricular cardiac muscle skinned by saponin (50 micrograms/ml). The size and shape of the RCC in skinned cardiac muscle were similar to those observed in intact cardiac muscle. The ATP-dependent Ca2-uptake pump in the sarcoplasmic reticulum (SR) was active at low temperature and could efficiently load the SR with Ca2+ even at 3 degrees C. Halothane reduced both RCC and caffeine contracture in a dose-dependent way when halothane treatment was applied before either RCC or caffeine. This action is consistent with halothane-induced depletion of the SR Ca2+. Under similar conditions, isoflurane inhibited RCC but had little effect on the caffeine contracture. This may suggest that rapid cooling and caffeine have different modes of action on the SR Ca(2+)-release channel. Our results provide further strong supporting evidence for differential inhibitory actions on a key intracellular organelle in cardiac muscle by two vapor anesthetic agents.

Effects of reduced external sodium concentration and multivalent cations on caffeine contractures in young ferret atrial trabeculae

The characteristics of caffeine (1.25–80 mM) transient contractures have been examined in small atrial trabeculae (diameters 50–250 μm) isolated from young (1 – 1.5 months) ferret hearts. In the control medium, the half-saturation constant and the maximum contracture strength (at infinite caffeine concentration) were 37.8 ± 10.2 mM and 0.9 ± 0.2 kN∙kg−1 (n = 11), respectively. The contractile response to caffeine was markedly enhanced following reduction of external sodium (70–0 mM). The perfusion of young ferret trabeculae with the sodium-free medium (up to 3 min) decreased the half-saturation constant by a factor of three (12.4 ± 1.6 mM, n = 8) with an increase in maximum contracture strength (1.09 ± 0.3 kN∙kg−1, n = 8). The effects of various divalent and trivalent cations have been tested on the 10 mM caffeine contracture in trabeculae perfused with Na-containing (140 mM) solution. The order of cation effectiveness is Gd3+ (half effect 0.04–0.07 mM) > Cd2+ (0.15–0.25 mM) > Ni2+ (2–2.5 mM) > Co2+ (7–7.5 mM) [Formula: see text] Mn2+. In conclusion, the present work has shown that in atrial trabeculae isolated from young ferret hearts, the strength of the caffeine contracture was markedly affected by the activity of the sarcolemmal Na–Ca exchange.Key words: caffeine, cardiac muscle, sarcoplasmic reticulum, sodium–calcium exchange, atrium, ferret.