Ryanodine and dihydropyridine binding patterns and ryanodine receptor mRNA levels in myopathic hamster heart.
We have determined the densities of sarcolemmal voltage-dependent Ca2+ channels (VDCC) and Ca(2+)-induced Ca2+ release channels (CICR) of sarcoplasmic reticulum (SR) in the cardiomyopathic hamster heart using [3H]PN-200 and [3H]ryanodine, respectively. Partially purified cardiac membrane preparations from myopathic animals exhibit a twofold higher capacity to bind both [3H]PN-200 and [3H]ryanodine. Crude particulate membrane fractions from normal and cardiomyopathic animals reveal no significant difference in receptor densities for [3H]PN-200, whereas densities for [3H]ryanodine binding sites and mRNA levels are significantly (P < 0.05) diminished in cardiomyopathic animals. Inhibition of [3H]ryanodine binding by either Ca2+ or Mg2+ (in mM) as well as temperature dependence for receptor activation for [3H]ryanodine (Q10) is not significantly different, whereas membranes isolated from cardiomyopathic hearts are 1.4-fold and threefold more sensitive to activation by doxorubicin and Ca2+ (in microM), respectively. Vesicles isolated from myopathic hearts are more sensitive to inhibition of Ca2+ uptake by doxorubicin. The higher densities of binding sites for [3H]PN-200 and [3H]ryanodine observed in partially purified membrane fractions from cardiomyopathic hearts are more likely the result of altered patterns with which T-tubule and CICR channels fractionate in preparations from cardiomyopathic hamster heart rather than transcriptional upregulation and may be a consequence of the deficiency in a dystrophin-associated glycoprotein recently identified. Downregulation and functional changes in CICR channels may alter SR Ca2+ transport and contribute to the progression of cardiomyopathy in the hamster.
Lachnit
W G
WG
Department of Molecular Biosciences, School of Veterinary Medicine, University of California, Davis 95616.
Phillips
M
M
Gayman
K J
KJ
Pessah
I N
IN
D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000235:genetics* / Q000502:physiology; D009202:Cardiomyopathies / Q000378:metabolism*; D006224:Cricetinae; D004095:Dihydropyridines / Q000378:metabolism*; D004317:Doxorubicin / Q000494:pharmacology; D004594:Electrophysiology; D017275:Isradipine / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics*; D009206:Myocardium / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012433:Ryanodine / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel
D015220:Calcium Channels; D004095:Dihydropyridines; D008565:Membrane Proteins; D009124:Muscle Proteins; D012333:RNA, Messenger; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; C038806:1,4-dihydropyridine; D004317:Doxorubicin; D002118:Calcium; D017275:Isradipine