Related Experiment Video
Updated: Aug 18, 2026

Focal Ca2+ Transient Detection in Smooth Muscle
Published on: June 29, 2009
Ca2+, cAMP, and changes in myosin phosphorylation during contraction of smooth muscle
Abstract:
Phosphorylation of myosin increases rapidly upon stimulation of an arterial smooth muscle. However, peak values are not maintained and phosphorylation declines, while active stress increases monotonically to a sustained steady state. The aim of this study was to determine the reason(s) for the transient change in myosin phosphorylation. Four hypotheses were considered: 1) reduced substrate, i.e., ATP depletion, 2) altered access of either the myosin kinase or phosphatase to the cross bridge, 3) reduced myosin kinase activity secondary to its phosphorylation by adenosine 3',5'-cyclic monophosphate-dependent protein kinase, and 4) reduced myoplasmic [Ca2+] during the contraction. Our results suggest that the most likely explanation is that there are two Ca2+-dependent regulatory processes: 1) myosin phosphorylation and 2) a second, unidentified site allowing stress maintenance with reduced cross-bridge cycling rates. A higher cell Ca2+ concentration appears to be necessary to activate myosin kinase and produce myosin phosphorylation than is needed for force maintenance. We suggest that agonist-induced Ca2+ transients, coupled with the differential Ca2+ sensitivity of the two regulatory systems, may explain the observed transient in myosin phosphorylation during a maintained contraction in smooth muscle.
Related Concept Videos
Cross-bridge Cycle
Actin and Myosin in Muscle Contraction
Muscle Contraction
Calmodulin-dependent Signaling
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
Excitation-Contraction Coupling in Skeletal Muscles
When an action potential...
Smooth Muscle Contraction
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...

