Fig. 8. Effect of BTP2 and BEL on Mn²⁺ entry triggered by the PLA₂ activator melittin. (A) Melittin (5 µM) was applied for 2 seconds onto isolated mdx^5cv fibers and Mn²⁺ entry was measured by the quench of Fura-2 fluorescence recorded at an excitation wavelength of 360 nm. Prior to melittin application, fibers were incubated with a solution containing 0.5 mM MnCl₂ and 1.7 mM CaCl₂. On the same graph are shown results from a control experiment and from experiments performed on fibers preincubated with either BTP2 (5 µM) for 10 minutes or BEL (10 µM) for 20 minutes (hatched trace). (B) Compiled data showing the percentage of fluorescence decrease 90 seconds after melittin application in control condition and when fibers had been preincubated with either BTP2 or BEL. Vertical hatched line on recordings shown in A indicates the time for measurements of fluorescence decrease. Numbers of fibers tested (from 2 mdx^5cv mice) are indicated on bar graphs. (C) Top: western blot of iPLA₂ performed on FDB and EDL (extensor digitorum longus) C57BL/6J and mdx^5cv muscles. Bottom: quantitative analysis of iPLA₂ amounts in FDB and EDL muscles from C57BL/6J and mdx^5cv mice. Numbers of mice used are indicated on bar graphs. (D) Left panel: western blot of SERCA1 performed on C57BL/6J and mdx^5cv FDB muscles. Right panel: quantitative analysis of SERCA1 amounts in FDB muscles from C57BL/6J and mdx^5cv mice. Numbers of mice used are indicated on bar graphs.