Figure 3. Demonstration that reversal of Na⁺-Ca²⁺ exchange with choline⁺ increased the fura-2 signal and enhanced refilling of the sarcoplasmic reticulum with Ca²⁺; both were inhibited by the L-type Ca²⁺ channel blocker diltiazem (Dilt).

Time courses are shown for aequorin-estimated [Ca²⁺]_i, fura-2-estimated [Ca²⁺]_i, the aequorin/fura-2 ratio and active stress. Data are from three sets of swine carotid medial tissues (n= 4–6 for each). All tissues had been treated with low extracellular Ca²⁺ and two histamine stimuli as described in Fig. 2. The first set had Ca²⁺ restored in a normal physiological saline solution (left panel, same data as in Fig. 2, left panel). The second set had Ca²⁺ restored in the presence of 10 μM diltiazem and 140 mM choline (substituted isosmotically for Na⁺, centre panel). The third set had Ca²⁺ restored in the presence of 140 mM choline (Chol; substituted isosmotically for Na⁺, right panel). Data are plotted as in Fig. 1.