A postulated role of the near amino-terminal domain of the ryanodine receptor in the regulation of the sarcoplasmic reticulum Ca2+ channel

To test the hypothesis that interactions among several putative domains of the ryanodine receptor (RyR) are involved in the regulation of its Ca2+ release channel, we synthesized several peptides corresponding to selected NH2-terminal regions of the RyR, We then examined their effects on ryanodine binding and Ca2+ release activities of the sarcoplasmic reticulum isolated from skeletal and cardiac muscle. Peptides 1-2s, 1-2c, and 1 enhanced ryanodine binding to cardiac RyR and induced a rapid Ca2+ release from cardiac SR in a dose-dependent manner. The order of the potency for the activation of the Ca2+ release channel was 1-2c > 1 > 1-2s, Interestingly, these peptides produced significant activation of the cardiac RyR at near zero or subactivating [Ca2+], indicating that the peptides enhanced the Ca2+ sensitivity of the channel. Peptides 1-2c, 1-2s, and 1 had virtually no effect on skeletal RyR, although occasional and variable extents of activation were observed in ryanodine binding assays performed at 36 degrees C, Peptide 3 affected neither cardiac nor skeletal RyR, We propose that domains 1 and 1-2 of the RyR, to which these activating peptides correspond, would interact with one or more other domains within the RyR (including presumably the Ca2+-binding domain) to regulate the Ca2+ channel.