Ischemia-reperfusion injury changes the dynamics of Ca²⁺-contraction coupling due to inotropic drugs in isolated hearts

Abstract

. Ischemia-reperfusion injury changes the dynamics of Ca 2ϩ -contraction coupling due to inotropic drugs in isolated hearts. J Appl Physiol 100: 940 -950, 2006. First published November 10, 2005 doi:10.1152/japplphysiol.00285.2005.-Positive inotropic drugs may attenuate or exacerbate the deleterious effects of ischemia and reperfusion (IR) injury on excitation-contraction coupling in hearts. We 1) quantified the phase-space relationship between simultaneously measured myoplasmic Ca 2ϩ concentration ([Ca 2ϩ ]) and isovolumetric left ventricular pressure (LVP) using indexes of loop area, orientation, and position; and 2) quantified cooperativity by linearly modeling the phase-space relationship between [Ca 2ϩ ] and rate of LVP development in intact hearts during administration of positive inotropic drugs before and after global IR injury. Unpaced, isolated guinea pig hearts were perfused at a constant pressure with Krebs-Ringer solution (37°C, 1.25 mM CaCl 2). [Ca 2ϩ ] was measured ratiometrically by indo 1 fluorescence by using a fiber-optic probe placed at the left ventricular free wall. LVP was measured by using a saline-filled latex balloon and transducer. Drugs were infused for 2 min, 30 min before, and for 2 min, 30 min after 30-min global ischemia. IR injury worsened Ca 2ϩ -contraction coupling, as seen from decreased orientation and repositioning of the loop rightward and downward and reduced cooperativity of contraction and relaxation with or without drugs. Dobutamine (4 M) worsened, whereas dopamine (8 M) improved Ca 2ϩ -contraction coupling before and after IR injury. Dobutamine and dopamine improved cooperativity of contraction and relaxation after IR injury, whereas only dopamine increased cooperativity of relaxation before IR injury. Digoxin (1 M) improved Ca 2ϩ -contraction coupling and cooperativity of contraction after but not before ischemia. Levosimendan (1 M) did not alter Ca 2ϩ -contraction coupling or cooperativity, despite producing concomitant increases in contractility, relaxation, and Ca 2ϩ flux before and after ischemia. Dynamic indexes based on LVP- [Ca 2ϩ ] diagrams (area, shape, position) can be used to identify and measure alterations in Ca 2ϩ -contraction coupling during administration of positive inotropic drugs in isolated hearts before and after IR injury.phase-space diagrams; cooperativity; guinea pigs; linear model POSITIVE INOTROPIC DRUGS ARE frequently administered to patients with left ventricular (LV) dysfunction to improve cardiac output (19). These agents mostly act by increasing myoplasmic Ca 2ϩ concentration ([Ca 2ϩ ]) ("upstream" mechanism) but may also enhance Ca 2ϩ binding to troponin C on the actin (TnCA) myofilament ("central" mechanism) or alter cross-bridge kinetics ("downstream" mechanism). Several classes of inotropic drugs act selectively through these mechanisms to improve Ca 2ϩ -contraction coupling. ␤-adrenergic and dopaminergic agonists (e.g., dobutamine and dopamine) increase myoplasmic cAMP concentrations to promote protein kinase-induced phosph...

Mathematical modelling of the calcium–left ventricular pressure relationship in the intact diabetic rat heart

“…The effects of b-adrenergic stimulation and subsequent protein kinase A (PKA)-mediated phosphorylation of several key proteins involved in Ca 2+contraction coupling on the kinetics of cross-bridge cycling and cooperativity are less clear. Assessment of the Ca 2+ -LVP relationship in intact doputamine-stimulated guinea pig hearts by a mathematical model suggested that rates of cross-bridge cycling are markedly increased when compared with baseline, whereas cooperativity was found to be decreased (Rhodes et al 2006). In addition, model analysis of the Ca 2+ -force relationship in isolated rat trabeculae suggested that isoproterenol reduces cooperativity (Dobrunz et al 1995), which is consistent with our finding of a decreased a¢ a upon isoproterenol stimulation.…”

“…The effects of β‐adrenergic stimulation and subsequent protein kinase A (PKA)‐mediated phosphorylation of several key proteins involved in Ca 2+ –contraction coupling on the kinetics of cross‐bridge cycling and cooperativity are less clear. Assessment of the Ca 2+ –LVP relationship in intact doputamine‐stimulated guinea pig hearts by a mathematical model suggested that rates of cross‐bridge cycling are markedly increased when compared with baseline, whereas cooperativity was found to be decreased (Rhodes et al. 2006).…”

Extra-matrix Mg2+ limits Ca2+ uptake and modulates Ca2+ uptake–independent respiration and redox state in cardiac isolated mitochondria

“…The physiological range of cytoplasmic [Ca 2+ ] e in cardiac cells fluctuates between about 100 and 400 nM with each heart beat and increases only moderately with inotropic stimulation (Rhodes et al 2006). In a normal cardiac cell, average [Ca 2+ ] m is about 150–200 nM (Riess et al 2002).…”

Ranolazine reduces Ca2+ overload and oxidative stress and improves mitochondrial integrity to protect against ischemia reperfusion injury in isolated hearts

“…For the c[Ca 2+ ] measurement, 100 µM MnCl 2 was perfused for 15 min by the end of the reperfusion to quench the cytosolic indo 1 signal. c[Ca 2+ ] was then calculated from the total [Ca 2+ ] after subtracting the mitochondrial component [44]. To estimate actual [Ca 2+ ] during the entire protocol, NADH autofluorescence was subtracted from the underlying changes in Ca 2+ fluorescent signals for each group [30,38,45].…”