Calcium sparks in human ventricular cardiomyocytes from patients with terminal heart failure

Abstract

Cardiomyocytes from terminally failing hearts display significant abnormalities in e–c-coupling, contractility and intracellular Ca2+ handling. This study is the first to demonstrate the influence of end-stage heart failure on specific properties of Ca2+ sparks in human ventricular cardiomyocytes. We investigated the frequency and characteristics of spontaneously arising Ca2+ sparks in single isolated human myocytes from terminally failing (HF) and non-failing (NF) control myocardium by using the Ca2+ indicator Fluo-3. The Ca2+ sparks were recorded by line-scan images along the longitudinal axis of the myocytes at a frequency of 250Hz. After loading the sarcoplasmic reticulum (SR) with Ca2+ by repetitive field stimulation (10 pulses at 1Hz) the frequency of the Ca2+ sparks immediately after stimulation (t = 0s) was reduced significantly in HF compared to NF (4.15 ± 0.42 for NF vs. 2.81 ± 0.20 for HF sparks s−1, P = 0.05). This difference was present constantly in line-scan recordings up to 15s duration (t = 15s: 2.75 ± 0.65 for NF vs. 1.36 ± 0.34 for HF sparks s−1, P = 0.05). The relative amplitude (F/F0) of Ca2+ sparks was also significantly lower in HF cardiomyocytes (1.33 ± 0.015 NF vs. 1.19 ± 0.003 HF, t = 0s) and during subsequent recordings of 15s. Significant differences between HF and NF were also present in calculations of specific spark properties. The time to peak was estimated at 25.75 ±0.88ms in HF and 18.68 ± 0.45ms in NF cardiomyocytes (P = 0.05). Half-time of decay was 66.48 ± 1.89ms (HF) vs. 44.15 ± 1.65ms (NF, P < 0.05), and the full width at half-maximum (FWHM) was 3.99 ± 0.06μm (HF) vs. 3.5 ± 0.07μm (NF, P < 0.05). These data support the hypothesis that even in the absence of cardiac disease, Ca2+ sparks from human cardiomyocytes differ from previous results of animal studies with respect to the time-to-peak, half-time of decay and FWHM. The role of elevated external Ca2+ in HF was studied by recording Ca2+ sparks in HF cardiomyocytes with 10mmol external Ca2+ concentration. Under these conditions, the average spark amplitude was increased from 1.19 ± 0.003 (F/F0, 2mmol Ca2+) to 1.26 ± 0.01 (F/F0, 10mmol Ca2+). We conclude that human heart failure causes distinct changes in Ca2+ spark frequency and characteristics comparable to results established in animal models of heart failure. A reduced Ca2+ load of the SR alone is unlikely to account for the observed differences between HF and NF and additional alterations in intracellular Ca2+ release mechanisms must be postulated.