Coordination of the contractile activity of bile canaliculi. Evidence from spontaneous contractions in vitro.

Rat hepatocytes, when isolated and maintained in primary culture, are capable of producing forceful contractions of their bile canaliculi, with contractions occurring on a regular basis once every 5.5 minutes. To determine whether the contraction of one bile canaliculus affected the contraction of a neighboring canaliculus, cinephotomicrographic studies of pairs of contiguous canaliculi were undertaken. The activity of 10 pairs of contiguous canaliculi, and 10 pairs of noncontiguous canaliculi which served as a control group, was recorded for a period of 12.5 hours at the rate of 1 frame every 15 seconds. Using frame-by-frame analysis of this period of observation, we determined the time of contraction of each of the canaliculi in the pairs. Cross-correlations were obtained for the contraction times of each of the 10 pairs of contiguous canaliculi and 10 control pairs. A peak in activity was found, with that peak occurring five frames or 75 seconds from the midline, whereas the noncontiguous controls showed no correlation in contractile activity. This finding indicates that, when one bile canaliculus contracts, a neighboring canaliculus is likely to contract after an interval of 1.25 minutes. That there is coordination of contractile activity of bile canaliculi suggests that, within the intact liver lobule, ordered motility function of the bile canaliculi may facilitate bile flow.