Figure 2. Simultaneous recording of inward current and Ca²⁺ influx.

SR Ca²⁺ release was blocked by treating the cells with 0.1 μm thapsigargin and 10 μm ryanodine. Na⁺ current was activated in the presence of 1 μm isoproterenol. A, activation of L-type Ca²⁺ current elicited an detectable Ca²⁺ influx signal with reduced amplitude due to the blockade of the SR release (note the absence of sparks). A potentiating effect of isoproterenol on the current amplitude and the Ca²⁺ signal is evident. B, analogous experiment with activation of the Na⁺ current. Note the change in the scale and the small amplitude of the Ca²⁺ signals. Traces are arranged in the same way as in Fig. 1.