INHIBITION OF SARCOTUBULAR CALCIUM TRANSPORT BY CAFFEINE - SPECIES AND TEMPERATURE DEPENDENCE

The effect of caffeine on calcium transport by isolated sarcotubular vesicles from rabbit and frog skeletal muscle was compared. At 25° the calcium uptake by rabbit vesicles which sedimented at 1500-10000 × g was only slightly inhibited by caffeine (1-10 mM). Increasing the temperature to 37° caused a marked increase in the caffeine sensitivity of the rabbit vesicles. The lighter vesicular fraction (10000-30000 × g) was relatively insensitive to caffeine at both temperatures. Frog vesicles at 25° were as sensitive to caffeine as the rabbit vesicles at 37°. This difference corresponds to the known differential sensitivity of amphibian and mammalian muscle to caffeine contracture. These results are consistent with the hypothesis that caffeine produces contracture through an inhibition of sarcotubular calcium transport. © 1969.