Fig. 1.

The effect of 100 μM piperine on the fluorescence of fast skeletal RLC-MDCC fibers. A single labeled fiber was mounted in a simple flow cell, and fluorescence was measured at two wavelengths. The ratio of the two intensities, which measures the population of the myosin heads in the SRX (18), is shown as a function of time. The fiber starts in rigor where the population of the SRX is zero. The ratio increases upon addition of ATP showing an increased population of the SRX. Subsequent addition of 100 μM piperine to the relaxing solution decreases the ratio showing that ∼60% of the myosin heads have transferred out of the SRX into the DRX. A subsequent wash with ATP shows that the effect of piperine is reversible. The structure of piperine is shown in the lower right.