Figure 3.

Effect of ventilation or mechanical stretch on Ca²⁺- and Sr²⁺-activation profiles of diaphragm fibers at term. (A) Representative data from twins where one lamb was delivered but not permitted to breathe (0 min), and the other lamb was allowed to establish ventilation and breathe for 40 min before autopsy. Breathing induces changes in the lower part of force–pSr curve that are similar to that occurring after 8 h of spontaneous ventilation (see Figure 2). (B) Representative data for Ca²⁺- and Sr²⁺-activation in a fiber from a term fetus where no breathing had occurred, and where the fiber was studied before (sarcomere length = 2.38 μm) and after (sarcomere length = 2.88 μm) mechanical stretch, in vitro. Stretch induces a change in the force–pSr curve similar to that induced by breathing.