Abstract
Thoracic duct (TD) lymphatics exhibit an increase in tonic activity as transmural pressure increases; whereas cervical lymphatics show an increase in phasic contraction frequency. We hypothesize that mechanical and biochemical characteristics of these lymphatic myofilaments will be different. The length‐tension relationships were determined for cervical and TD lymphatics. Cervical and TD lymphatics exhibited a biphasic response to maximal activation with high K++PSS+Substance P. TD generated larger active peak and plateau tensions than did cervical lymphatics (in mN/mm; peak tension: 0.65±0.06 vs. 0.43±0.01 P<0.03; plateau tension: 0.54±0.06 vs 0.25±0.04 p<0.01). pCa‐tension relationships were also determined in a‐toxin permeabilized lymphatics. While maximal peak tension in a‐toxin permeabilized TD was greater than cervical lymphatics (0.76±0.08 vs. 0.50+0.07 p<0.02), plateau tension was not significantly different (0.56±0.07 vs. 0.41±0.07 P<0.15). The Ca2+sensitivity (pCa50) and cooperativity of TD and cervical lymphatics were not significantly different (5.93±0.02 vs 5.86±0.06 & 1.73±0.11 vs. 1.49±0.09). Thus the differences in the mechanical characteristics between TD and cervical lymphatics are not attributable to variations in pCa50 and cooperativity; other Ca2+‐dependent or ‐independent mechanisms may play important roles in these lymphatics. Supported by NIH HL80526 & LRF.
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