AJP - Endocrinology and Metabolism, Vol 270, Issue 2 E203-E208, Copyright © 1996 by American Physiological Society

ARTICLES

Oxytocin-mediated recruitment of slowly cycling cross bridges and isometric force in rat myometrium

A. L. Ruzycky and B. T. Ameredes
Magee Women's Research Institute, University of Pittsburgh, Pennsylvania 15213, USA.

The relationship between cross-bridge cycling rate and isometric stress was investigated in rat myometrium. Stress production by myometrial strips was measured under resting, K+ depolarization, and oxytocin-stimulated conditions. Cross-bridge cycling rates were determined from measurements of maximal unloaded shortening velocity, using the quick-release method. Force redevelopment after the quick release was used as an index of cross-bridge attachment. With maximal K+ stimulation, stress increased with increased cross-bridge cycling (+76%; P < 0.05) and attached cross bridges (+112%; P < 0.05). Addition of oxytocin during K+ stimulation further increased stress (+30%; P < 0.05). With this force component, the cross-bridge cycling rate decreased (-60%; P < 0.05) similar to that under resting conditions. Attached cross-bridges did not increase with this additional stress. The results suggest two distinct mechanisms mediating myometrial contractions. One requires elevated intracellular calcium and rapidly cycling cross bridges. The other mechanism may be independent of calcium and appears to be mediated by slowly cycling cross bridges, supporting greater unit stress.

This article has been cited by other articles:

				K. McKillen, S. Thornton, and C. W. Taylor Oxytocin increases the [Ca2+]i sensitivity of human myometrium during the falling phase of phasic contractions Am J Physiol Endocrinol Metab, February 1, 1999; 276(2): E345 - E351. [Abstract] [Full Text] [PDF]