L-type cardiac calcium channels in doxorubicin cardiomyopathy in rats morphological, biochemical, and functional correlations.

Abstract

Doxorubicin (DXR) is an effective antitumor agent in a wide spectrum of neoplasms. Chronic treatment is associated with cardiomyopathy and characteristic myocardial ultrastructural changes, which include swelling of the t tubules. Accordingly, we investigated excitation-contraction coupling in cardiomyopathic rat heart resulting from chronic DXR treatment. Using the whole-cell patch clamp technique, we studied the L-type calcium channel in single cells enzymatically isolated from normal (CTRL) and DXR rat hearts. Despite similar cell dimensions, the total membrane capacitance was significantly smaller in the DXR cells (138±9 pF) than in the CTRL cells (169±11 pF) (mean±SEM, n = 9, P < 0.05). The mean current and the current density-voltage relationships of the CTRL and the DXR cells were significantly different (n = 9, P < 0.001) with the maximal peak L-type calcium current (Ic) density increased from 6A±0.9 in CIRL cells to 10.5±2.4 .A/cm2 in the DXR cells (P < 0.05). There was no shift either in the currentvoltage relationship or the steady-state inactivation curve in the two cell groups. However, the fast time constant of inactivation was increased at a membrane voltage of -10 to 10 mV. Calcium channel antagonist equilibrium binding assays using 13H1 PN200-110 revealed no difference in the maximal receptor binding capacity (CrRL, 194±27 and DXR 211±24 fmol/mg protein; P > 0.05, n = 6) and in receptor affinity (CTRL, 0.15±0.05 and DXR 0.13±0.03 nM; P < 0.05). These data suggest that a decrease in effective capacitance might be associated with t-tubular damage. Despite this decrease, IcJ was increased in the DXR cells. Such an increase may result from an alteration in the properties of the calcium channels and/or recruitment of "hibernating" channels in the remaining surface and t-tubular membranes. (J. Clin. Invest. 1991. 87:2108-2113

Doxorubicin-induced reactive oxygen species generation and intracellular Ca2+increase are reciprocally modulated in rat cardiomyocytes

“…Statistical significance was set at P＜0.05. (Keung et al, 1991). Therefore, effect of a L-type Ca 2+ channel blocker, nifedipine, on DOX-induced Ca 2+ signal was examined.…”

“…In this study, the molecular basis of DOX-induced intracellular Ca 2+ regulation has been examined (Keung et al, 1991), inhibits Na + -Ca 2+ exchanger (Caroni et al, 1981), or releases Ca 2+ from SR (Zorzato et al, 1985;Kim et al, 1989). Our results have shown that DOX-mediated increase of [Ca 2+ ]i is due to a release of Ca 2+ from SR through ROS-mediated opening of RyR.…”

“…Direct effects of the drug on various Ca 2+ channels have also been observed. DOX increases the open probability of sarcoplasmic reticulum (SR) calcium release channels (Zorzato et al, 1985;Kim et al, 1989), inhibits Na + -Ca 2+ exchanger (Caroni et al, 1981) or activates L-type cardiac calcium channel (Keung et al, 1991). All of these DOX effects on Ca 2+ channels can lead to Ca 2+ overload of cardiac cells that may render mitochondrial calcium overloading, resulting in alteration of energy metabolism and generation of reactive oxygen species (ROS).…”

Doxorubicin Cardiotoxicity

“…[2][3][4] However, the present study showed that myocardial alterations in DOX-induced cardiotoxicity were less prominent than those in previous reports. We used a rat model in DOX-induced cardiomyopathy according to the method of Keung et al 22 with some modification. However, the sex of rats, the route and span of drug administration, and the duration until sacrifice after final drug administration were different from previous papers.…”

“…The investigation was performed in accordance with the Guide for the Care and use of Laboratory Animals published by the US National Institutes of Health (NIH publication No 85-23, revised 1985). DOX-induced cardiomyopathy was induced as previously described by Keung et al 22 with some modifications. DOX was administered ip at a dose of 2.5 mg/kg once a week for 10 weeks.…”