Gl. Wright et al., VASCULAR SMOOTH-MUSCLE CONTRACTILE PROPERTIES IN THE PIGEON, Comparative biochemistry and physiology. Part A, Physiology, 111(1), 1995, pp. 107-115
Rings excised from the upper portion (aortic arch to A. Celiaca) and l
ower portion (A. celiaca to A. renalis cranialis) of the pigeon aorta
showed distinctly different contractile properties, Both tissues exhib
ited significant temperature sensitivity over the range of 45-22 degre
es C with optimal temperature at 40-42 degrees C. The optimal preload
was approximately 3 g and 8 g for the lower and upper segments of the
aorta, respectively. The two segments differed significantly in their
sensitivity to potassium depolarization. Disruption of the endothelium
did not alter the sensitivity to potassium depolarization, but reduce
d the maximal response. The response of both segments to norepinephrin
e was quite variable, and showed evidence of decreased responsiveness
with repeated contraction or prolonged exposure to the compound. Both
segments showed extracellular calcium dependency. Significant tension,
development in zero calcium buffer, was observed for both segments, b
ut was particularly pronounced in the upper aorta. Cytochalasin D, an
inhibitor of actin polymerization, blocked slow tension increase in bo
th segments, but was particularly effective in rings from the lower se
gment of aorta. The results indicate that the regulation of contractil
e function in pigeon aorta differs in important respects from that of
mammalian tissue.