Key result
Increasing stimulus frequency from 1 to 4 Hz in isolated rat cardiomyocytes caused a significant decrease in shortening percentage and relaxation times, while ATP and PKA activation increased contraction amplitude.
Why the study?
Rodent heart rate is 4-6 Hz, but 1 Hz is typically used in isolated cardiomyocyte studies; contraction parameters and the roles of ATP and PKA across frequencies remained to be examined.
In isolated rat cardiomyocytes, the force-stimulus frequency relationship is negative, and energy metabolism and the beta-adrenergic system may mediate this relationship.
Animal data on cardiomyocyte frequency responses remain hypothesis-generating; human validation required before clinical translation.
The physiological heart rate of rodents is around 4-6 Hz, although a stimulus frequency of 1 Hz is generally used in isolated cardiomyocytes to study changes in the contraction-relaxation cycle in cardiac muscle physiology and pathophysiology. Our study investigated the contraction parameters in isolated cardiomyocytes at 1, 2 and 4 Hz stimulation, and the roles of ATP and protein kinase A (PKA) in the force-frequency relationship in isolated cardiomyocytes. The contraction of the cell and intracellular Ca2+ changes were recorded simultaneously during cell stimulation by applying pulses of 6-8 V amplitude with frequencies of 1, 2 and 4 Hz. The increase in stimulus frequency caused a significant decrease in the percentage of shortening, relaxation times, slowing of the relaxation rate, and a significant increase in diastolic Ca2+ levels, but had no effect on the contraction rate and Ca2+ transients. Administration of ATP and N6-benzoyladenosine-3'-5'-cyclic monophosphate (6-BNZ-cAMP) caused an increase in contraction amplitude and speed which were proportional to the stimulus frequency but had no effect on the relaxation times. The experimental results show that the force-stimulus frequency has a negative correlation in isolated myocytes and that energy metabolism and the ?-adrenergic system may be responsible for this relationship.
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Öztürk et al. (2023) studied Force-frequency relationship in cardiac muscle. Stimulus frequency (1, 2, and 4 Hz), ATP, and 6-BNZ-cAMP administration was evaluated on Contraction parameters and intracellular Ca2+ changes. Increasing stimulus frequency from 1 to 4 Hz in isolated rat cardiomyocytes caused a significant decrease in shortening percentage and relaxation times, while ATP and PKA activation increased contraction amplitude.
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