Influence of Ca2+ on force redevelopment kinetics in skinned rat myocardium.
The influence of Ca2+ on isometric force kinetics was studied in skinned rat ventricular trabeculae by measuring the kinetics of force redevelopment after a transient decrease in force. Two protocols were employed to rapidly detach cycling myosin cross-bridges: a large-amplitude muscle length ramp followed by a restretch back to the original length or a 4% segment length step. During the recovery of force, the length of the central region of the muscle was controlled by using a segment marker technique and software feedback control. Tension redevelopment was fit by a rising exponential governed by the rate constant ktr for the ramp/restretch protocol and kstep for the step protocol. ktr and kstep averaged 7.06 s-1 and 15.7 s-1, respectively, at 15 degrees C; neither ktr nor kstep increased with the level of Ca2+ activation. Similar results were found at submaximum Ca2+ levels when sarcomere length control by laser diffraction was used. The lack of activation dependence of ktr contrasts with results from fast skeletal fibers, in which ktr varies 10-fold from low to high activation levels, and suggests that Ca2+ does not modulate the kinetics of cross-bridge attachment or detachment in mammalian cardiac muscle.
Hancock
W O
WO
Center for Bioengineering, University of Washington, Seattle 98195, USA.
Martyn
D A
DA
Huntsman
L L
LL
Gordon
A M
AM
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects* / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism*; D009218:Myosins / Q000737:chemistry / Q000502:physiology; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D013696:Temperature
D010710:Phosphates; D000255:Adenosine Triphosphate; D009218:Myosins; D002118:Calcium