Key result
Hypercapnic acidosis reduces maximum isometric tension but not shortening velocity, whereas lower calcium decreases both.
Why the study?
Does hypercapnic acidosis alter force-sarcomere length and force-velocity relations compared to lowering extracellular calcium in rat cardiac trabeculae?
Does hypercapnic acidosis alter force-sarcomere length and force-velocity relations compared to lowering extracellular calcium in rat cardiac trabeculae?
Acidosis reduces maximum isometric tension without affecting maximum unloaded sarcomere shortening velocity, likely due to competition between Ca++ and H+ ions for myofilament binding.
Distinguishes hypercapnic acidosis effects on sarcomere function from low calcium in rats; leaves open relevance to intact heart or clinical acidosis.
The effect of hypercapnic acidosis was compared with that of lowering extracellular calcium concentration ([Ca++]o) in rat cardiac trabeculae. The relations between force and sarcomere length and between force and velocity were studied. Sarcomere length was measured by means of laser diffraction techniques and sarcomere shortening velocity by means of isovelocity releases. The curve representing the relation between force and sarcomere length shifted from convex towards the ordinate (pH 7.35) to convex towards the abscissa (pH 6.68) as after [Ca++]o had been reduced from 1.5 to 0.3 mmol X litre-1. Increasing [Ca++]o at low pH from 1.5 to 4.0 mmol X litre-1 allowed the shape of the relation to be restored, but force values failed to return to control values. The relation between force and pH over the range 6.22-7.94 was also tested. During steady low pH maximum unloaded sarcomere shortening velocity was not significantly different from control values whereas it was decreased at low [Ca++]o. Under both conditions maximum isometric tension (Po) was reduced. The results are consistent with the hypothesis that H+ ions cause a shift of the force-p Ca curve to the right at all sarcomere lengths, as a result of competition between Ca++ and H+ ions for binding to the myofilaments.
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Ricciardi et al. (1986) studied Normal rat cardiac muscle. Hypercapnic acidosis vs. Lowered extracellular calcium concentration (0.3 mmol/L) and control pH (7.35) was evaluated on Force-sarcomere length and force-velocity relations. Hypercapnic acidosis reduced maximum isometric tension but did not significantly alter maximum unloaded sarcomere shortening velocity, whereas lowered extracellular calcium decreased both.
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