Mouse Ventricular Cardiomyocytes

OxLDL-Induced Reduction of Cardiomyocyte Cell-Shortening Requires PCSK9

PCSK9 functions in liver LDL metabolism which plays a vital role in maintaining cardiovascular health. The fact that PCSK9 shows expression in cardiomyocytes and is regulated by oxidized LDL (oxLDL) demonstrates possible non-hepatic roles in cardiac cell function.

To investigate whether endogenously expressed PCSK9 alters cell shortening of adult ventricular cardiomyocytes, Wolf et al. isolated adult ventricular cardiomyocytes from PCSK9−/−- as well as PCSK9+/+-mice. Comparison between both strains revealed no obvious difference (Fig. 1). Cardiomyocytes from both strains were cultivated under serum-free conditions and also incubated for 24 h with oxLDL (5 µM). Thereafter function was measured by load-free cell shortening. The cardiomyocytes showed reduced relative cell shortening after oxLDL (5 µM) incubation (Fig. 1a). as well as contraction (Fig. 1b) and relaxation velocities (Fig. 1b). PCS9+/+-cardiomyocytes showed no significant change under the same conditions when isolated from PCSK9−/−-mice (Fig. 1a–c). The absence of PCSK9 resulted in faster contraction and relaxation speeds in cardiomyocytes treated with oxLDL (Fig. 1b  and  c).

Fig. 1. Effect of oxLDL on load-free cell shortening of isolated cardiomyocytes derived from PCSK9−/−- and PCSK9+/+-mice (Wolf A, Schreckenberg R, et al., 2020).

Mepivacaine Reduces Calcium Transients in Isolated Murine Ventricular Cardiomyocytes

Mepivacaine impacts cardiac function, causing arrhythmias by altering Na+ current in heart cells. Given its observed myocardial depression, Mosqueira et al. aim to investigate how mepivacaine influences Ca²⁺ transients in isolated mouse ventricular cardiomyocytes to better understand its negative inotropic effect.

To determine the IC₅₀ of mepivacaine, the peak area from Ca²⁺ transients was analyzed across various concentrations: 0, 10, 20, 40, 50, 75, and 100 μM (Fig. 2a and b). The IC₅₀ was estimated at 50.85 ± 6.79 μM, so 50 μM was used for subsequent testing. At this concentration, mepivacaine significantly reduced Ca²⁺ transient aspects, including baseline (control: 356.8 ± 42.12 nM; mepivacaine: 132.2 ± 14.55 nM, p < 0.05; Fig. 3b), peak area (control: 401.7 ± 63.09 nMs; mepivacaine: 72.14 ± 10.46 nMs, p < 0.05; Fig. 3c), and D₅₀ (control: 457.1 ± 47.16 ms; mepivacaine: 284.5 ± 22.71 ms, p < 0.05; Fig. 3d), while the total duration remained unchanged (p > 0.05; Fig. 3e). Reduction in peak (Fig. 4a), slope (Fig. 4b), and time to peak (Fig. 4c) were also observed. However, re-uptake measures showed no significant effect on tau and time to uptake.

Fig. 2. Representative Ca²⁺ transients' traces to the dose-response effect of mepivacaine at 0, 10, 20, 40, 50, 75 and 100 μM (Mosqueira M, Aykut G, et al., 2020).

Fig. 3. Representative Ca²⁺ transients trace demonstrating the inhibitory effect of mepivacaine at half maximal inhibitory concentration (IC₅₀) on in isolated mouse ventricular cardiomyocytes (Mosqueira M, Aykut G, et al., 2020).

Fig. 4. Summarized data for the effect of mepivacaine at IC₅₀ on Ca²⁺ release's biophysical parameters obtained from Ca²⁺ transients (Mosqueira M, Aykut G, et al., 2020).