Caffeine-induced Contraction Research Articles

Caffeine- and potassium-induced contractures of frog striated muscle fibers in hypertonic solutions.

The effect of hypertonic solutions on the caffeine- and KCl-induced contractures of isolated fibers of frog skeletal muscle was tested. Hypertonic solutions, twice the normal osmotic strength, prepared by adding NaCl or sucrose, potentiate the caffeine-induced contractures. The fibers may develop tensions of 3.6 kg/cm(2) of fiber transverse section. The same hypertonic medium reduced the peak tension of KCl-induced contractures. Thus the hypertonic condition does not affect the contractile mechanism itself. These findings give further support to the view that the differential effect of hypertonic solution is on the excitation-contraction coupling mechanism. Extracellular calcium is not essentially required for the first few of a series of caffeine-induced contractures either in hypertonic or in isotonic solutions.

Caffeine-induced contracture and potentiation of contraction in normal and denervated rat muscle

Caffeine-induced contracture and potentiation of contraction in normal and denervated rat muscle

DISSOCIATION OF ELECTRICAL AND MECHANICAL EVENTS IN DENERVATED FROG SKELETAL MUSCLE.

In chronically denervated sartorius muscles of frog, the mechanical responses to direct electrical stimulations, caffeine-induced contracture, and the duration of plateau of the active state have been studied. The ATP-induced contraction of glycerol-extracted muscle fibers, which were prepared from denervated and contralateral innervated muscles, have been also observed.1. The mechanical responses to direct electrical stimulations were gradually decreased with the lapse of time after denervation.2. Even at the end of 30 days after denervation the resting and the action potentials of denervated muscle fibers were normal.3. The developed tension due to 2 mM ATP in glycerol-extracted muscle fibers prepared from the 7 weeks-denervated muscles was not different from that in contralateral innervated muscle fibers.4. Both the shape and the size of caffeine-induced contracture in denervated muscles were the same as those in the contralateral innervated ones.5. The duration of plateau of the active state in denervated muscles was ranged from 22.6 to 29.2 msec. at about 18°C. These results were not different from those of the contralateral innervated ones.6. Based on the above-mentioned results it is concluded that the E-C coupling process of frog sartorius muscle is depressed due to denervation.

Dissociation of electrical and mechanical activity in the frog's sciatic-sartorius muscle preparation caused by prolonged immersion in Ringer solution.

The effects of the immersion of nerve-muscle preparations of frog in Ringer solution on the excitation and contraction phenomena were followed up to 24 hours.1. The twitch responses of the muscle to indirect and direct electrical stimulations decreased to quite similar degree until 8 hours after immersion. However, it was observed that the twitch responses to indirect stimulations reduced more prominently after 8 hours.2. Until at least 8 hours after immersion, no changes in action potentials of the whole muscles elicited by indirect stimulations were observed.3. Not only the action potentials of the nerve trunks, but also the resting and action potentials of the directly stimulated muscle fibres were quite similar to those in the control even at 24 hours after immersion.4. There were no differences in size and shape of the caffeine-induced contractures between the muscle immersed in Ringer solution for 24 hours and the control.5. In the muscle surviving for 24 hours in Ringer solution, the threshold concentration of Ach to produce contractures was about 10 times higher than that in the control.6. It is concluded that the failure of the E-C coupling processes in the surviving nerve-muscle preparations starts in earlier stage prior to functional disturbances of the end-plate, and remains incomplete even after 24 hours when the end-plate transmission fails completely.