Arg615Cys substitution in pig skeletal ryanodine receptors increases activation of single channels by a segment of the skeletal DHPR II-III loop

The effect of peptides, corresponding to sequences in the skeletal muscle dihydropyridine receptor II-III loop, on Ca2+ release from sarcoplasmic reticulum (SR) and on ryanodine receptor (RyR) calcium release channels have been compared in preparations from normal and malignant hyperthermia (MH)-susceptible pigs. Peptide A (Thr(671)-Leu(690); 36 muM) enhanced the rate of Ca2+ release from normal SR (SRN) and from SR of MH-susceptible muscle (SRMH) by 10 +/- 3.2 nmole/mg/min and 76 +/- 9.7 nmole/mg/min, respectively. Ca2+ release from SRN or SRMH was not increased by control peptide NB (Gly(689)-Lys(708)). AS (scrambled A sequence; 36 muM) did not alter Ca2+ release from SRN, but increased release from SRMH by 29 +/- 4.9 nmoles/mg/min. RyR channels from MH-susceptible muscle (RyR(MH)) were up to about fourfold more strongly activated by peptide A (greater than or equal to1 nM) than normal RyR channels (RyR(N)) at -40 mV. Neither NE or AS activated RyR(N). RyR(MH) showed an similar to1.8-fold increase in mean current with 30 muM AS. Inhibition at +40 mV was stronger in RyR(MH) and seen with peptide A (greater than or equal to0.6 muM) and AS (greater than or equal to0.6 muM), but not NB. These results show that the Arg(615)Cys substitution in RyR(MH) has multiple effects on RyRs. We speculate that enhanced DHPR activation of RyRs may contribute to increased Ca2+ release from SR in MH-susceptible muscle.