Fig. 3.

Differences in calcium signaling and vascular tone of pressurized wild-type (WT) and iPLA₂β knockout (KO) mesenteric arterioles stimulated with PE and ACh. Changes in intracellular calcium concentration (measured as the ratio of the fura-2 fluorescence at 340/380 nm) and vessel diameter were determined as described in materials and methods. A and B: representative tracings of fura-2 calcium fluorescence ratios (upper trace, left axis) and diameter changes (lower trace, right axis) for a WT (A) and a KO (B) vessel. C: absolute vessel diameter responses and calcium ratios in all vessels from WT (n = 5) and KO (n = 5) mice indicate that maximum (Max) and steady-state constriction responses to PE (100 μmol/l) were significant (‡P < 0.05 from respective control, ANOVA) with the constriction significantly enhanced in KO vessels compared with WT (*P < 0.05, ANOVA). The basal control fura-2 calcium ratio was significantly lower in KO vessels compared with WT control (†P < 0.05). Vessels from KO mice did not dilate in response to ACh [10 μmol/l; not significant (NS)] in contrast with normal vessel dilation in WT controls (¶P < 0.05 between steady-state diameter and ACh diameter). In addition, dilation of WT vessel coincided with a decrease in the calcium ratio (¶), whereas the calcium ratio in KO vessels was not significant (NS). D: although most relative diameter and calcium responses reflect the absolute values, the initial relative calcium response was much higher in KO vessels (§P < 0.05).