AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 2 195-G200, Copyright © 1986 by American Physiological Society
Muscarinic receptor size on smooth muscle cells and membranes
S. M. Collins, C. Y. Jung and A. K. Grover
The loss of [3H]quinuclidinyl benzilate ([3H]QNB) binding following
high-energy radiation was used to compare the muscarinic receptor size on
single smooth muscle cells isolated by collagenase digestion from the
canine stomach and on plasma membranes derived from intact gastric smooth
muscle without exposure to exogenous proteolysis. Radiation inactivation of
galactose oxidase (68 kdaltons), yeast alcohol dehydrogenase (160
kdaltons), and pyruvate kinase (224 kdaltons) activities were used as
molecular-weight standards. Radiation inactivation of [3H]QNB binding to
rat brain membranes, which gave a target size of 86 kdaltons, served as an
additional control. In isolated smooth muscle cells, the calculated size of
the muscarinic receptor was 80 +/- 8 kdaltons. In contrast, in a smooth
muscle enriched plasma membrane preparation, muscarinic receptor size was
significantly smaller at 45 +/- 3 kdaltons. Larger molecular sizes were
obtained either in the presence of protease inhibitors (62 +/- 4 kdaltons)
or by using a crude membrane preparation of gastric smooth muscle 86 +/- 7
kdaltons).
