ryanodine and Cardiomyopathy--Hypertrophic

Prodynorphin mRNA and dynorphin B expression have been previously shown to be greatly increased in cardiac myocytes of BIO 14.6 cardiomyopathic hamsters. Here we report that exogenous dynorphin B induced a dose-dependent increase in prodynorphin mRNA levels and stimulated prodynorphin gene transcription in normal hamster myocytes. Similar responses were elicited by the synthetic selective kappa opioid receptor agonist U-50,488H. These effects were counteracted by the kappa opioid receptor antagonist Mr-1452 and were not observed in the presence of chelerythrine or calphostin C, two specific protein kinase C (PKC) inhibitors. Treatment of cardiomyopathic cells with Mr-1452 significantly decreased both prodynorphin mRNA levels and prodynorphin gene transcription. In control myocytes, dynorphin B induced the translocation of PKC-alpha to the nucleus and increased nuclear PKC activity without affecting the expression of PKC-delta, -epsilon, or -zeta. Acute release of either U-50,488H or dyn B over single normal or cardiomyopathic cells transiently increased the cytosolic Ca2+ concentration. A sustained treatment with each opioid agonist increased the cytosolic Ca2+ level for a more prolonged period in cardiomyopathic than in control myocytes and led to a depletion of Ca2+ from the sarcoplasmic reticulum in both groups of cells. The possibility that prodynorphin gene expression may affect the function of the cardiomyopathic cell through an autocrine mechanism is discussed.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Animals; Calcium; Cardiomyopathy, Hypertrophic; Cell Compartmentation; Cell Nucleus; Cricetinae; Cytosol; Dynorphins; Endorphins; Enkephalins; Enzyme Inhibitors; Gene Expression; Mesocricetus; Myocardium; Protein Kinase C; Protein Precursors; Pyrrolidines; Receptors, Opioid, kappa; Ryanodine; Sarcoplasmic Reticulum

Calcium overload has been linked to the development of cardiomyopathy in the cardiomyopathic (CM) hamster, but the site or sites of the lesion remain obscure. To determine whether the number of sarcoplasmic reticulum (SR) calcium release channels (ryanodine receptors) changes in the CM heart, we compared the density (Bmax) and affinity (Kd) of [3H]-ryanodine binding sites in heavy SR fractions from 40-65 day-old normal and CM hamster hearts. Results showed that the Bmax was significantly increased in CM heart when compared to normal (Bmax = 2489 +/- 159 fmol/mg protein in normal heart and 3360 +/- 223 fmol/mg protein in CM heart, mean +/- S.E., P = 0.01). [3H]-Ryanodine bound to a single, high affinity site in SR from both normal and CM hearts; values for Kd were similar in both groups. Sensitivity of [3H]-ryanodine binding to Ca2+ was unchanged, but the density of binding was increased at all Ca2+ concentrations which potentiated binding in CM heart. Similarly, potentiation of [3H]ryanodine binding by ATP and inhibition of binding by Mg2+ were intact in membranes from CM heart. Results demonstrate that the density [3H]-ryanodine receptors is increased in SR from CM hearts early in the development of cardiomyopathy, although the properties of these receptors are unchanged. This suggests an increase in the amount or velocity of Ca2+ release from SR may contribute to the development of Ca2+ overload in this model of cardiomyopathy.

Topics: Age Factors; Animals; Calcium Channels; Cardiomyopathy, Hypertrophic; Cricetinae; Heart Failure; Male; Mesocricetus; Muscle Proteins; Ryanodine; Ryanodine Receptor Calcium Release Channel; Sarcoplasmic Reticulum; Up-Regulation