Effects of Amino-Terminal Disease-Associated Mutations on the CICR Activity of RyR1 Channel

Type 1 ryanodine receptor (RyR1) is a Ca2+ release channel in the sarcoplasmic reticulum and plays a pivotal role in excitation-contraction coupling in skeletal muscle. RyR1 is the major target for muscle diseases, e.g., malignant hyperthermia (MH) and central core disease (CCD). To date, over 200 mutations have been identified in the RyR1 gene of MH and CCD patients. It is widely believed that MH and CCD mutations cause hyperactivation of the Ca2+-induced Ca2+ release (CICR), resulting in abnormal Ca2+ homeostasis in skeletal muscle. CICR shows biphasic Ca2+ dependence, thus the activity can be determined by three parameters: sensitivity to activating Ca2+, sensitivity to inactivating Ca2+, and the gain (i.e., peak activity). However, it remains unclear how the disease-associated mutations affects these parameters. In this study, we expressed several RyR1 channels carrying different MH/CCD mutations at amino-terminal region in HEK cells and tested their CICR by live-cell Ca2+ imaging and [3H]ryanodine binding. Our results suggest that the amino-terminal disease-associated mutations divergently affects the parameters of CICR depending on the sites for mutation. The underlying molecular mechanism will be discussed.