Divergent kinetics of 201Tl and 99mTc-SESTAMIBI in cultured chick ventricular myocytes during ATP depletion.

Abstract

BACKGROUND Thallous chloride (201Tl) and hexakis(2-methoxyisobutyl isonitrile) technetium (I) (99mTc-SESTAMIBI) are myocardial perfusion imaging agents with biological properties that also reflect tissue viability. Initial myocellular uptake rates of 201Tl reflect activity of Na,K-ATPase, whereas those of 99mTc-SESTAMIBI reflect mean plasma membrane potential. METHODS AND RESULTS To better understand the mechanistic responses of these tracers to myocellular injury, cultured chick embryo cardiac myocytes were metabolically inhibited in iodoacetate (1 mM) and rotenone (10 microM) for up to 2 hours, and initial uptake rates of each agent were determined at successive intervals along with correlative cellular contents of ATP, sodium, and potassium and lactate dehydrogenase release. ATP content fell from 30.5 +/- 1.4 to 2.7 +/- 0.9 nmol.(mg protein)-1 within 2 minutes, whereas sodium and potassium contents ran down their thermodynamic gradients more slowly (t 1/2 approximately 60 minutes). Modestly severe cell injury was produced at 2 hours as estimated by lactate dehydrogenase release (18% of total). Initial uptake rates of 201Tl declined from 6.9 +/- 0.8 to 4.0 +/- 0.4 fmol.(mg protein)-1.(nMo)-1.(min)-1 by 20 minutes and remained depressed and ouabain (100 microM)-insensitive at 30 +/- 13% of control. Conversely, initial uptake rates of 99mTc-SESTAMIBI increased from 10.6 +/- 0.8 to 15.0 +/- 0.6 fmol.(mg protein)-1.(nMo)-1.(min)-1 within 10 minutes, remained elevated for 40-60 minutes, and later declined to low values. Injury-induced enhancement of initial uptake rates of 99mTc-SESTAMIBI were insensitive to ouabain (100 microM), carbonyl cyanide-m-chlorophenyl hydrazone (5 microM), and valinomycin (1 microgram/ml) but were significantly inhibited by 130 mM Ko buffer, Ba2+ (1 mM), glybenclamide (100 microM), and quinacrine (10 microM). CONCLUSIONS Uptake rates of 201Tl monotonically decline, correlating with Na-K pump inhibition from ATP depletion. Conversely, uptake rates of 99mTc-SESTAMIBI at first increase above control for 40-60 minutes, indicating a mean plasma membrane hyperpolarization possibly resulting from opening of ATP-sensitive and arachidonic acid-activated potassium channels, before declining to low values with more severe cell injury. Correlative non-flow-dependent relations between 201Tl and 99mTc-SESTAMIBI contain information regarding the degree of myocellular injury.

99 mTc-MIBI washout as a complementary factor in the evaluation of idiopathic dilated cardiomyopathy (IDCM) using myocardial perfusion imaging

“…In this study, although differences in the early and delayed H/M ratio were not statistically significant between the two groups, the myocardial 99 mTc-sestamibi WR in the target group (29.13 ± 6.68%) were significantly higher than those in the control group (P B 0.01). This is consistent with a previous report stating that the initial 99 m Tc-MIBI uptake rate (at 40-60 min) was higher in cultured chick embryo cardiac myocytes with mild to moderate metabolic injury than in those without such injury [20].…”

Characterization of Phosphine Complexes of Technetium(III) as Transport Substrates of the Multidrug Resistance P-Glycoprotein and Functional Markers of P-Glycoprotein at the Blood−Brain Barrier

“…The residual net accumulation of each radiopharmaceutical under isoelectric membrane potential is one measure of nonspecific adsorption of hydrophobic cationic complexes to lipid compartments in cells (28,34). Prior studies have established that Tc-Sestamibi is a Nernstian probe of membrane potential with minimal adsorptive binding to lipid bilayers (28,35,36). Thus, in the presence of high K + and valinomycin, residual uptake of Tc-Sestamibi maps intracellular water space (28,35).…”

Non-Q-wave myocardial infarction: impaired myocardial energy metabolism in regions with reduced 99mTc-MIBI accumulation

“…However, the MIBI uptake also correlated with energy metabolism, implying that other factors may contribute to these alterations. Although previous studies on cell cultures have shown that the uptake of MIBI by myocytes decreases only when the intracellular pool of ATP is severely reduced [23], other cause-and-effect relationships between energy metabolism and MIBI accumulation are possible. MIBI, a lipophilic cation, is taken up by myocardial cells and sequestered in mitochondria in an energy-dependent manner in response to transmembrane potentials [24,25].…”