FIGURE 8.

Effect of BZ194 on sarcoplasmic reticular-luminal Ca²⁺ concentration ([Ca²⁺]_SR) during electrical and β-adrenergic stimulation. Murine ventricular cardiac myocytes were loaded with 5 μm mag-Fura-2/AM for 30 min at 37 °C and 2% CO₂ (v/v). Time for uptake into the SR and hydrolysis of the ester and incubation with either 0.25% vehicle DMSO (control) or 1 mm BZ194 (BZ) was 60 min at 37 °C and 2% CO₂ (v/v). Incubation time with 200 nm isoproterenol was 5 min directly before the measurement. Ca²⁺ imaging was carried out as described under “Experimental Procedures.” Fluorescence at 380 nm was measured, and the ratio of F₀/F was calculated. a, typical transients obtained at 0.5 s⁻¹ electrical pacing (gray arrows) and subsequent addition of 10 mm caffeine (caf) (black arrows) are shown. b shows the percentage of cells with only one transient [Ca²⁺]_lu decrease versus cells showing more than one transient [Ca²⁺]_lu decrease. Numbers within the bars represent the sample size. Asterisks denote statistical significant differences (**, p = 0.0081; *, p = 0.0158; Mann-Whitney rank sum test).