AJP - Gastrointestinal and Liver Physiology, Vol 245, Issue 1 44-G53, Copyright © 1983 by American Physiological Society
Role of protein phosphorylation in regulating rat submandibular mucin secretion
D. O. Quissell, L. M. Deisher and K. A. Barzen
The possible involvement of protein phosphorylation during beta-adrenergic
receptor stimulation in rat submandibular gland was investigated in vitro
using a dispersed cell preparation. (-)-Isoproterenol, a beta-adrenergic
agonist, or dibutyryl cAMP stimulation was associated with an enhanced
phosphorylation of three protein bands having apparent molecular weights of
34,000, 26,000, and 21,000, respectively. (-)-Propranolol, a
beta-adrenergic antagonist, inhibited the phosphorylation of the three
proteins during beta-adrenergic stimulation but not during dibutyryl cAMP
stimulation. The three proteins were not fragments of a
higher-molecular-weight protein. Subcellular fractionation using
differential centrifugation, fractionation in an aqueous two-phase polymer
system, and discontinuous sucrose gradient ultracentrifugation coupled with
marker enzyme analysis indicated that all three proteins were enriched in
the same subfractions: a heavy plasma membrane fraction and a fraction
containing plasma membrane and Golgi membrane material. The extent of
protein phosphorylation for all three proteins increased as a function of
time and dose after beta-adrenergic stimulation. After 20 min of maximal
beta-adrenergic stimulation, the addition of a beta-adrenergic blocker
caused a time-dependent decrease in the 32P content of all three proteins.
Pure cholinergic or pure alpha-adrenergic receptor stimulation had no
effect on the 32P content of the three proteins. These data are consistent
with a role for cAMP-mediated protein phosphorylation during mucin
secretion from rat submandibular cells.
