Decreased ca2+ sensitivity of isometric tension in skinned cardiac myocytes from tail suspended rats. Dunlap, Alexander W., Donald B. Thomason, Vandana Menon, and Polly A. Hofmann. Department of Physiology and Biophysics, University of Tennessee, Memphis, TN 38163
APStracts 3:0005A, 1996.
Tail suspension in rats causes a cephalic shift in blood resulting in a volume load on the heart similar to that observed during microgravity space flight or mild heart failure. The present study determined the influence of increased cardiac hemodynamic load on myofilament isometric tension as a function of [Ca2+] in skinned cardiac myocytes of control and 7 day head-down tilt Sprague-Dawley rats. Isometric force of single skinned myocytes was measured by attaching cells with adhesive to a force transducer and piezoelectric translator. A significant decrease in the Ca2+ sensitivity of tension was observed in cardiac myocytes from suspended, pCa50 of 5.83 0.03, as compared to control rats, pCa50 of 5.94 0.03. Maximum tension generation and slope of the tension-pCa relation were unaffected by head-down tilt. Electrophoretic analysis of myofilament proteins indicate differences in expression of proteins in the 50-60 kDa and 100-120 kDa ranges; immunoblot analysis of tubulin (50 kDa) expression indicates no change in the ratio of -tubulin to light chain 1 or tropomyosin. Decreased force-producing ability at a given submaximum [Ca2+] in cardiac myocytes from suspended rats suggests a decrease in contractility possibly due to changes in cardiac myofilament protein expression following chronic, elevated volume load on the heart. 

Received 21 July 1995; accepted in final form 15 December 1995.
APS Manuscript Number A798-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96