Ca(2+)-induced Ca2+ release in myocytes from dyspedic mice lacking the type-1 ryanodine receptor.

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Abstract
While subtypes 1 and 2 of the ryanodine receptor (RyR) function as intracellular Ca2+ release channels, little is known about the function of the third subtype (RyR‐3), first identified in brain. Myocytes from mice homozygous for a targeted mutation in the RyR‐1 gene (dyspedic mice) can now be used for a study on the function of RyR‐3, which is predominantly expressed in these cells according to our reverse transcription‐polymerase chain reaction analysis. We here demonstrate in these myocytes caffeine‐, ryanodine‐ and adenine nucleotide‐sensitive Ca(2+)‐induced Ca2+ release with approximately 10 times lower sensitivity to Ca2+ than that of RyR‐1. Although RyR‐3 does not mediate excitation‐contraction coupling of the skeletal muscle type, we propose that RyR‐3 may induce intracellular Ca2+ release in response to a Ca2+ rise with a high threshold.