Figure 2.

Extracellular Ca²⁺ is vital for 5-hydroxytryptamine (5-HT)-elicited pulmonary arterial contraction. Isometric tension recording of pulmonary arterial rings, constricted in the absence of 2 mmol/L extracellular Ca²⁺ (black), or in the presence of extracellular Ca²⁺ (gray) from (A) normoxic and (B) LTH fetal lambs. Tracings are plotted in relation to maximal contraction from an initial 10 μmol/L 5-HT stimulation (%T_{5-HT Control}). (C) Bars indicate mean ± SEM of %T_{5-HT Control} in the presence or absence of extracellular Ca²⁺ for pulmonary arteries from normoxic (open) and LTH (solid) fetuses. ***Denotes significant difference between the presence and absence of extracellular Ca²⁺ by an unpaired Student t test (P < .001). LTH indicates long-term hypoxia; SEM, standard error of the mean.