1. Strips of bovine tracheal muscle and rabbit aorta produced sustained contractions on perfusion with
Krebs solution made twice normal strength by addition of
sucrose. The
contractures were relaxed on return to normal
Krebs solution. 2. Similar
contractures were produced by tracheal muscle strips in Krebs solutions made twice normal strength by addition of
galactose,
glucose or NaCl whereas
urea caused only a transient contraction. 3. In twice normal strength
Krebs solution (
sucrose added) the basal tension of rat portal vein and guinea-pig taenia coli was increased. Spontaneous mechanical activity was maintained, but the frequency of contractions was reduced. 4. The hypertonic
contracture of bovine trachea in twice normal strength
Krebs solution (
sucrose added) was reduced by 15% by omission of Ca from the bathing fluid (0.1 mmol/l
EGTA added). Severe Ca depletion, by prolonged washing in Ca-free Krebs with 12.5 mmol/l
EGTA and
Carbachol added, resulted in a 77% reduction in the hypertonic
contracture. 5. In twice normal
Krebs solution (
sucrose added), the hypertonic
contracture was partially relaxed by
isoprenaline (4 x 10(-6) mol/l); the contractile response to
carbachol was reduced; the contractile response to high-K
Krebs solution was maintained. 6.
Atropine (5 x 10(-7) mol/l) abolished the contractile response to
carbachol, but had no effect on the hypertonic
contracture. 7. It is suggested that the contraction of bovine tracheal strips in
hypertonic solutions is mainly due to activation of the contractile myofilaments rather than simple cell shrinkage.
Hypertonic solutions may also interfere with some steps in the excitation-contraction coupling sequence.