Figure 6. Demonstration that removal of extracellular [Ca²⁺] reduced the aequorin signal and reduces [Ca²⁺]_i inhomogeneity; this suggests that Ca²⁺ influx was responsible for [Ca²⁺]_i inhomogeneity in resting smooth muscle.

The data show the response to removal of extracellular Ca²⁺ with and without CPA. Time courses are shown for aequorin-estimated [Ca²⁺]_i, fura-2-estimated [Ca²⁺]_i, the aequorin/fura-2 ratio and active stress. Data are means ±s.e.m. from two sets of swine carotid medial tissues (n= 4–6 for each). Extracellular Ca²⁺ was nominally removed at 10 min by changing the bathing solution to a solution with no added Ca²⁺. At 10.5 min, one set of the tissues was treated with 10 μM CPA (○), and the other set of tissues was not treated with CPA (•). Data were collected at 1 s intervals and averaged over 10 s for plotting. Symbols without error bars reflect errors less than the size of the symbol. Only stress from the fura-2 experiments is shown for clarity (the aequorin stress data were similar).