AJP - Cell Physiology, Vol 258, Issue 2 C282-C288, Copyright © 1990 by American Physiological Society
Modification of temperature dependence of myofilament Ca sensitivity by troponin C replacement
S. M. Harrison and D. M. Bers
Division of Biomedical Sciences, University of California, Riverside 92521.
The Ca sensitivity of chemically skinned right ventricular trabeculae from
the rat heart was determined at 22 and 8 degrees C. Endogenous troponin C
(TnC) was then extracted with EDTA and replaced with either bovine cardiac
TnC or rabbit fast-twitch skeletal TnC. The temperature dependence of
myofilament Ca sensitivity was then reevaluated. Cooling native cardiac
tissue from 22 to 8 degrees C reduced the pCa (-log10 [Ca2+]), generating
half-maximal tension (K1/2) from 5.20 +/- 0.07 to 4.89 +/- 0.08 (SD, n =
14), and also reduced maximum Ca-activated force to 33 +/- 6% of its value
at 22 degrees C. After extraction of endogenous TnC and reconstitution with
cardiac TnC, cooling from 22 to 8 degrees C caused a similar shift in mean
K1/2 from 4.93 +/- 0.08 to 4.69 +/- 0.06 (n = 7). When skeletal TnC was
reconstituted into TnC-extracted ventricular fibers, cooling from 22 to 8
degrees C led to a much smaller mean shift in K1/2 from 4.88 +/- 0.07 to
4.78 +/- 0.04 (n = 7). The results show that the magnitude of the
cooling-induced shift in myofilament Ca sensitivity observed in the native
state (or after reconstitution with cardiac TnC) is significantly reduced
if the fiber is reconstituted with skeletal TnC (P less than 0.001). This
indicates that the temperature dependence of myofilament Ca sensitivity of
cardiac muscle can be modified by incorporation of skeletal TnC. Thus Ca
binding to TnC plays an important role in determining the temperature
dependence of myofilament Ca sensitivity.
