Calcium in Smooth Muscle from the Opossum Esophagus

Abstract

Summary

Transverse muscle strips were cut from four segments of the opossum esophagus. Segment I was the segment of smooth muscle bordering on the striated muscle proximally and Segment IV was the distal segment which includes the lower esophageal sphincter. Segments II and III were the two central fourths of the smooth muscle esophagus. The tissue calcium content was determined in strips coming from the four segments after ashing and extraction of strips in concentrated HCl-HNO₃. The calcium content (in mmole/kg wet muscle ± 1 SE) was 2.70 ± 0.1 in Segment I, 2.8 ± 0.3 in Segment II, 2.6 ± 0.3 in Segment III, and 2.6 ± 0.3 in Segment IV after 2 hr of incubation.

After incubation of strips coming from the four segments, efflux of ⁴⁵Ca was measured during 15 two-min periods. Efflux was rapid at first with a halftime of 5 min and slowed after three periods to a halftime of 29 min. In all nine animals tested, efflux from the lower esophageal sphincter was slower than that from muscle of the esophageal body. Thus, calcium content in the smooth muscle esophagus does not depend on location. However, tonic esophageal smooth muscle (sphincter) exchanges calcium less rapidly with the bathing medium than the phasic-type smooth muscle from the body of the opossum esophagus.

The authors are grateful to Dr. James Christensen for his interest and advice. The research funds came from National Institutes of Health Research Grant AM 11242 and in part from National Institutes of Health Research Grant AM 09892-13.