Caffeine contractures were registered on fibre bundle preparations of frog m. semitendinosus. The drug was applied to muscles in normal Ringer for 30 min in concentrations of 3-40 mM. Biphasic contractures were found in all cases above mechanical threshold concentration of caffeine (2.35 mM. calculated value). Parameter values belonging to the two contracture phases (amplitude, delta l1 l2; time, t1 t2) were analysed by computer programmes in correlation with caffeine concentration. It was found that 1. both contracture phases have the same concentration threshold of caffeine; 2. a caffeine-binding site with K(d)=24.6 mM can be supposed in the surface membrane being responsible for the induction of the first contracture phase of caffeine in the muscle; 3. caffeine has a concentration-dependent action on the surface membrane binding site with a tendency of muscles to contract to zero length at infinite caffeine concentration; 4. the speed of caffeine action is practically equal to the solution exchange emphasizing the action site at the surface membrane of the muscle (sarcolemma and T-tubule membrane); 5. the second caffeine contracture phase develops with maximal amplitude above contracture threshold concentration, during which muscles contract to about 40% of their slack length; this corresponds to a sarcomere length less than that of the myosin filament, consequently, a shortening of this filament must also take plase; 6. the concentration dependence of the second contracture phase results in a monotonic decrease of t2 with increasing caffeine concentration. A possibility for the mechanism of caffeine action through binding to proteins involved in the regulation of intracellular calcium level is discussed.
|Number of pages||9|
|Journal||Acta biologica Academiae Scientiarum Hungaricae|
|Publication status||Published - Dec 1 1979|
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)