Figure 1. Repeatability of hypoxic response in rat IPA, and dependence on external Ca²⁺.

A, IPAs were preconstricted with 3 μM PGF_2α and challenged with hypoxia for 45 min before being washed (○). After 60 min the process was repeated (•). The value shown for phase I after 5 min hypoxia is the mean of the peak tension obtained during this phase. It can be seen that the second (experimental) response was identical to the first (control) response. The symbols represent the mean ±s.e.m. of five arteries. Where error bars are not shown, the error is smaller than the symbol. B, HPV in IPAs under control conditions (○, 3 μM PGF_2α), and in 0 Ca²⁺ PSS containing 1 mM EGTA (•, 100 μM PGF_2α). Removal of extracellular Ca²⁺ completely inhibited HPV (n= 3, P < 0.001 for every point).