Key result
Simulated microgravity reduces myocyte calcium sensitivity in rats compared to controls.
Why the study?
Tail suspension in rats causes a volume load on the heart similar to microgravity or mild heart failure, but its influence on myofilament isometric tension and Ca2+ sensitivity was unclear.
Does 7-day head-down tilt (tail suspension) decrease Ca2+ sensitivity of isometric tension in skinned cardiac myocytes from Sprague-Dawley rats?
Does 7-day head-down tilt (tail suspension) decrease Ca2+ sensitivity of isometric tension in skinned cardiac myocytes from Sprague-Dawley rats?
Absolute Event Rate: 5.83% vs 5.94%
Chronic elevated volume load on the heart, simulated by 7-day head-down tilt in rats, decreases Ca2+ sensitivity of isometric tension in cardiac myocytes, potentially reducing contractility.
Decreased myofilament Ca2+ sensitivity after 7-day simulated microgravity in rats; leaves open relevance to human HF or spaceflight and requires prospective validation.
Tail suspension in rats causes a cephalic shift in blood, resulting in a volume load on the heart similar to that observed during microgravity spaceflight or mild heart failure. The present study determined the influence of increased cardiac hemodynamic load on myofilament isometric tension as a function of Ca2+ concentration 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 rats [pCa of half-maximal tension (pCa50) of 5.83 +/- 0.03] compared with control rats (pCa50 of 5.94 +/- 0.03). Maximum tension generation and slope of the tension-pCa relationship were unaffected by head-down tilt. Electrophoretic analysis of myofilament proteins indicates differences in expression of proteins in the 50-60 and 100-120 kDa ranges; immunoblot analysis of tubulin (50 kDa) expression indicates no change in the ratio of beta-tubulin to light chain 1 or tropomyosin. Decreased force-producing ability at a given submaximum Ca2+ concentration 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.
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Dunlap et al. (1996) studied Volume load on the heart (simulated microgravity or mild heart failure). Head-down tilt tail suspension vs. Control rats was evaluated on Ca2+ sensitivity of tension (pCa50). 7-day head-down tilt tail suspension significantly decreased the Ca2+ sensitivity of tension in rat cardiac myocytes (pCa50 5.83 vs 5.94 in controls).
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