ISSN:
1573-2657
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Summary The goal of this study was to investigate how an increase in the extracellular K+ (K0 +) concentration immediately after fatigue affects the recovery of the resting potential, the twitch and tetanic contraction of frog sartorius muscle to further understand the role of K+ in the mechanism of fatigue. Resting potentials were measured with conventional microelectrodes. Twitch and tetanic contractions were elicited by field stimulation. All muscles were fatigued with tetanic contractions at a rate of one contraction per second for 3 min while being exposed to 3 mmole l-1 K0 +. During fatigue development the resting potential decreased by 16 mV (control group and pH0 7.2, extracellular pH), while the decrease in the twitch force was 32.8%, compared to 79.3% for the tetanic force, and 84.6% for the maximum rate of force development of the tetanus. Fatigued muscles were also unable to maintain a plateau phase during a tetanus: force declined by 14.8% during this phase. During the recovery period under control conditions (3 mmole l-1 K0 +), all four parameters returned to their pre-fatigue values, the recovery of the plateau phase was the fastest (10 min), while that of the twitch force was the slowest (80 min). When K0 + was increased to 7.5 or 9.5 mmole l-1 immediately after fatigue, the recovery rate of the tetanic force and plateau phase was reduced. The maximum rate of force development of the tetanus, however, recovered at a faster rate than control muscles. The recovery of the twitch force was also increased above that of control when K0 + was increased to 9.0 mmole l-1 (a concentration which maximally potentiates the twitch force of unfatigued muscle). Frog sartorius muscles were also tested at pH0 6.4, a pH0 which inhibits force recovery. At that pH0 the effects of K0 + were similar to those observed at pH0 7.2. It is concluded that the role of K+ in muscle fatigue is more complex and may not involve just a contribution to the decrease in force during fatigue development, but may also contribute to an increase in force development under some conditions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00122116
Permalink