DYSPEDIC MOUSE SKELETAL-MUSCLE EXPRESSES MAJOR ELEMENTS OF THE TRIADIC JUNCTION BUT LACKS DETECTABLE RYANODINE RECEPTOR PROTEIN AND FUNCTION

The ry1(53) dyspedic mouse contains two disrupted alleles for ryanodin e receptor type 1 (skeletal isoform of ryanodine receptor; Ry(1)R) res ulting in perinatal death, In the present study, whole skeletal muscle homogenates and sucrose gradient-purified junctional sarcoplasmic ret iculum from neonatal wild-type and dyspedic mice were assayed for bioc hemical and functional markers, Equilibrium binding experiments perfor med with 1-120 nM [H-3]ryanodine reveal saturable high and low affinit y binding to membrane preparations from wild-type mice, but not to pre parations from dyspedic mice. Binding experiments performed with [H-3] PN200 show a a fold reduction in [H-3]PN200 binding capacity in dysped ic muscle, compared to age matched wild-type muscle, with no change in receptor affinity. The presence or absence of proteins known to be cr itical for normal ryanodine receptor/Ca2+ channel complex function was assessed by Western blot analysis. Results indicate that FKBP-12, DHP R alpha 1, triadin, calsequestrin, SERCA1 (sarco(endo)plasmic reticulu m Ca2+ ATPase), and skeletal muscle myosin heavy chain are present in both dyspedic and wild-type muscle. Only wild-type membranes showed im munoreactivity toward Ry(1)R antibody. Neither dyspedic nor wild-type mouse muscle showed detectable immunoreactivity toward Ry(2)R or Ry(3) R antibodies, even after sucrose gradient purification of sarcoplasmic reticulum, These results indicate that proteins critical for ryanodin e receptor function are expressed in dyspedic skeletal muscle in the a bsence of Ry(1)R, Ca2+ transport measurements show that membranes from wild-type controls, but not dyspedic mice, release Ca2+ upon exposure to ryanodine. Dyspedic mice and cells derived from them serve as exce llent homologous expression systems in which to study how Ry(1)R struc ture relates to function.