AJP - Cell Physiology, Vol 232, Issue 3 144-C154, Copyright © 1977 by American Physiological Society
Characteristics of response of isolated smooth muscle cells to cholinergic drugs
F. S. Fay and J. J. Singer
The contractile responses of suspensions of isolated smooth muscle cells
from the stomach muscularis of Bufo marinus were assessed with a Coulter
counter. Contractile responses of strips from the same tissue were recorded
isotonically. Suspensions of isolated smooth muscle cells exhibit a
dose-dependent graded response to cholinergic agonists. The intact tissue
has a lower sensitivity than the isolated cells to acetycholine but a
higher sensitivity to carbachol. The higher sensitivity of isolated cells
to acetycholine probably reflected decreased efficiency of cholinesterases
upon removal of diffusion barriers. Because the isolated smooth muscle
cells have affinity constants for atropine (K1 equals 0.07 +/- 0.02NM) and
carbachol (9.5 +/- 3.7 muM) similar to that in this and other intact
tissues, the affinity of the cholinergic receptor appears unaffected by
cell isolation. The rate constant for dissociation (k2) of atropine was
estimated from the slowing of response to carbachol by atropine; k2 in the
isolated cells is 100 times larger than seen in intact tissues. Further
insight into the interaction of cholinergic substances with their smooth
muscle receptors might by obtained using this system. The isolated cells
contain intact receptors, and diffusion limitations inherent to intact
tissue have been removed.
