FIGURE 9.

Contractile response of airway and arteriole to Ca²⁺ oscillations. (A) Length changes of an airway (black) and arteriole (gray) SMC to a step increase in agonist a and frequency at the time points indicated. The initial Ca²⁺ oscillations (1 spike/min) in the absence of agonist cause strong variations only in the length of the airway SMC. Ca²⁺ oscillations with higher frequencies (>5 spike/min) cause continuous contraction in both airway and arteriole SMC. (B) Relative area changes in response to calcium oscillations (solid lines) and a constant signal of the same average [Ca²⁺]_i (dashed lines). We assume that six and three SMCs form an airway and arteriole, respectively. The phase difference in the calcium oscillations between cells in the airway and arteriole is chosen to be 2π/6 and 2π/3, respectively. Ca²⁺ oscillations are modeled as a periodic piecewise linear function. The spike widths are 20, 5, and 2.5 s at a = 0, 0.3, and 1.2, respectively. The peak [Ca²⁺]_i is 1.3 μM at a = 0, and 0.6 μM at a = 0.3 and 1.2. Basal [Ca²⁺]_i is 0.2 μM; initial [Ca²⁺]_i is 0.1 μM. The constant signal [Ca²⁺]_i with and without agonist is 0.4 and 0.56 μM, respectively.