In isolated rat ventricular trabeculae at near-physiological external Ca2+ (1 mM), a positive force-frequency relationship was demonstrated at all temperatures (24, 30, and 37 degrees C).
The positive force-frequency relationship in rat ventricular trabeculae is driven by frequency-dependent sarcoplasmic reticulum Ca2+ loading, which saturates at high frequencies or Ca2+ overload, leading to a negative relationship.
The isometric force-frequency relationship of isolated rat ventricular trabeculae (diameter 6 Hz at 30 degreesC) at 1 mM Ca2+o or at low frequencies at 8 mM Ca2+o. The twitch and Ca2+ transient became shorter as stimulation frequency increased; these changes were related to changes in systolic, rather than diastolic, Ca2+i and were not blocked by inhibitors of Ca2+/calmodulin-dependent protein kinase II. The positive force-frequency relationship of rat trabeculae was caused by a frequency-dependent loading of the sarcoplasmic reticulum (SR) with Ca2+. We suggest that at high frequencies, or under conditions of Ca2+ overload, this loading saturates. Processes that tend to decrease SR Ca2+ release will then predominate, resulting in a negative force-frequency relationship.
Layland et al. (Fri,) reported a other. Stimulation frequencies (0.1-12 Hz) at varying temperatures and Ca2+ concentrations was evaluated on Isometric force-frequency relationship and intracellular Ca2+ concentration. In isolated rat ventricular trabeculae at near-physiological external Ca2+ (1 mM), a positive force-frequency relationship was demonstrated at all temperatures (24, 30, and 37 degrees C).
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