Figure 4. Effect of [Mg²⁺]_p on I_Ca in high phosphorylation conditions.

A, current–voltage relationships for I_Ca in myocytes dialysed with 0.2 mm and 1.8 mm[Mg²⁺]_p in control (continuous curves) and high phosphorylation conditions (dashed curves) in the absence and presence of 10 μm forskolin (FSK), 300 μm IBMX and 50 μm OA, respectively, when [Ca²⁺]_o was set at 0.5 mm. Currents were recorded at 5 min after break-through into the whole-cell patch-clamp configuration. Data are means and s.e.m., with the number of experiments indicated in parentheses. B, tracings of typical I_Ca records at a test potential of 0 mV in rat ventricular myocytes dialysed with 0.2 mm (•) and 1.8 mm[Mg²⁺]_p (▴) in control conditions, and 0.2 mm (○) and 1.8 mm[Mg²⁺]_p (▵) in high phosphorylation conditions.