Prolonged force increase following a high-frequency burst is not due to a sustained elevation of [Ca2+]i |
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Authors: | Abbate F Bruton J D De Haan A Westerblad H |
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Institution: | Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, 1081 BT Amsterdam, The Netherlands. Fabio.Abbate@fyfa.ki.se |
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Abstract: | A brief high-frequency burst of action potentials results in a sustained force increase in skeletal muscle. The present study investigates whether this force potentiation is the result of a sustained increase of the free myoplasmic Ca2+] (Ca2+]i). Single fibers from mouse flexor brevis muscles were stimulated with three impulses at 150 Hz (triplet) at the start of a 350-ms tetanus or in the middle of a 700-ms tetanus; the stimulation frequency of the rest of the tetanus ranged from 20 to 60 Hz. After the triplet, force was significantly (P < 0.05) increased between 17 and 20% when the triplet was given at the start of the tetanus and between 5 and 18% when the triplet was given in the middle (n = 7). However, during this potentiation, Ca2+]i was not consistently increased. Hence, the increased force following a high-frequency burst is likely due to changes in the myofibrillar properties. |
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