Fig. 9.

Bradykinin (BK) activated stretch-sensitive units when muscle activity was abolished in Ca²⁺-free Krebs solution. Effects of 1 μM bradykinin on a stretch-activated mechanoreceptors in rectum from an untreated animal. Bradykinin evoked increased circular muscle contractility and several bursts of firing in the stretch-sensitive mechanoreceptors (unit 1 and unit 2) and also activated stretch-insensitive unit 3. In Ca²⁺-free solution (containing 3.6 mM Mg²⁺), muscle activity was abolished but bradykinin still evoked several bursts of firing in the stretch-sensitive unit 1, but not 2, and activated stretch-insensitive unit 3.