AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 5 710-G717, Copyright © 1986 by American Physiological Society
Suggestion of a role for calmodulin and phosphorylation in regulation of rabbit ileal electrolyte transport: effects of promethazine
M. E. Cohen, G. W. Sharp and M. Donowitz
Suggestion of a role for protein phosphorylation in the regulation of
intestinal active NaCl transport was found by studying the effects of low
concentrations of promethazine on Ca2+-calmodulin (CaM)-dependent protein
phosphorylation of ileal microvillus membranes and on active ileal
electrolyte transport. Ca2+-CaM increased the phosphorylation of six
microvillus peptides (Mr 137,000, 116,000, 77,000, 58,000, 53,000, and
50,000) in a concentration-dependent manner. Promethazine inhibited the
Ca2+-CaM-induced increases in each of these phosphorylations. The effect of
promethazine was concentration dependent, with concentrations of 5-12
microM (mean 8 microM) causing 50% inhibition. Promethazine also caused a
concentration-dependent increase in net Cl absorption and decrease in the
ileal short-circuit current, with 9 microM promethazine causing a change in
short-circuit current 50% of maximum. The promethazine effect on
microvillus membrane phosphorylation was specific, since neither cAMP- and
cGMP-induced phosphorylation in the microvillus membrane nor the
stimulation by Ca2+-CaM of myosin light chain kinase phosphorylation of
myosin light chain were affected by promethazine. The similar, and unusual
sensitivity to low concentrations of promethazine on ileal microvillus
membrane phosphorylation increased by Ca2+-CaM and on ileal electrolyte
transport is consistent with Ca2+-CaM-dependent microvillus membrane
phosphorylation being involved in the regulation of active electrolyte
transport in ileal absorptive cells.
