AJP - Gastrointestinal and Liver Physiology, Vol 253, Issue 3 378-G382, Copyright © 1987 by American Physiological Society
Distribution of beta-adrenoceptors associated with cAMP-generating system in cat colon
K. Taniyama, T. Kuno and C. Tanaka
The localization of beta-adrenoceptor associated with the adenosine
3',5'-cyclic monophosphate (cAMP)-generating system was determined by an
assessment of the smooth muscle cell contractility and by assay of cAMP in
individual layers of the cat colon. Isoproterenol inhibited the
acetylcholine (ACh)-induced contractions of isolated longitudinal and
circular muscle cells in a dose-dependent manner. The response of the
longitudinal muscle cells to isoproterenol was double that seen in the
circular muscle cells, and this inhibition was antagonized by sotalol. The
basal content of cAMP was 3.42 pmol/mg protein in longitudinal muscle
layers, 3.09 pmol/mg protein in circular muscle layers, and 2.75 pmol/mg
protein in Auerbach's plexus. Isoproterenol produced a dose-dependent
elevation of cAMP levels in longitudinal and circular muscle layers, which
were antagonized by sotalol and potentiated by theophylline. By contrast,
isoproterenol had no effect on cAMP in Auerbach's plexus. Phenylephrine did
not alter the cAMP levels in any layer. Therefore, beta-adrenoceptors
associated with the cAMP-generating system probably exist in the
longitudinal and circular muscles of the cat colon.
