Force maintenance in smooth muscle: analysis using sinusoidal perturbations.
The "latch state" or force maintenance may be due to the emergence of a distinct set of dephosphorylated, slowly cycling "latch" cross-bridges, slowing of the overall cross-bridge cycling rate, or a non-cross-bridge contribution. This was investigated by sinusoidally oscillating strips of intact rabbit portal vein or aorta. Tissue strips were activated with KCl depolarization, resulting in a sustained increase of MLC(20) phosphorylation or 10 microM phenylephrine, resulting in a transient increase in MLC(20) phosphorylation. Stiffness was calculated from the force response to a small, sine-wave oscillation in muscle length (1-100 Hz). The results produced a 3-dimensional plot of stiffness versus the frequency of oscillation (Hz) versus time (s), or stiffness distribution profile. During KCl depolarization, the stiffness distribution profile displayed a shift toward lower frequencies, suggesting a general slowing in the overall cross-bridge cycling rate during force maintenance. On the other hand, phenylephrine stimulation did not display a significant change in the stiffness distribution profile, suggesting that the overall cross-bridge cycling rate did not significantly change during force maintenance.
Rhee
Albert Y
AY
Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Avenue, Cleveland, OH 44106-4970, USA.
Brozovich
Frank V
FV
D000818:Animals; D001011:Aorta; D001696:Biomechanical Phenomena; D004548:Elasticity; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009131:Muscle, Smooth, Vascular / Q000737:chemistry* / Q000187:drug effects / Q000502:physiology*; D018994:Myosin Light Chains / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D010766:Phosphorylation; D011169:Portal Vein; D011189:Potassium Chloride / Q000378:metabolism / Q000494:pharmacology; D011817:Rabbits; D024745:Smooth Muscle Myosins / Q000378:metabolism
D018994:Myosin Light Chains; D010656:Phenylephrine; D011189:Potassium Chloride; D024745:Smooth Muscle Myosins