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Departments of 1 Medicine and 2 Physiology, The University of Western Ontario, and 3 Lawson Research Institute, St. Joseph's Health Centre, London, Ontario, Canada N6A 4V2
Receptor
characterization in human esophageal smooth muscle is limited by tissue
availability. We used human esophageal smooth muscle cells in culture
to examine the expression and function of muscarinic receptors. Primary
cultures were established using cells isolated by enzymatic digestion
of longitudinal muscle (LM) and circular muscle (CM) obtained from
patients undergoing esophagectomy for cancer. Cultured cells grew to
confluence after 10-14 days in medium containing 10% fetal bovine
serum and stained positively for anti-smooth muscle specific
-actin.
mRNA encoding muscarinic receptor subtypes
M1-M5 was identified by RT-PCR. The
expression of corresponding protein for all five subtypes was confirmed
by immunoblotting and immunocytochemistry. Functional responses were assessed by measuring free intracellular Ca2+ concentration
([Ca2+]i) using fura 2 fluorescence. Basal
[Ca2+]i, which was 135 ± 22 nM,
increased transiently to 543 ± 29 nM in response to 10 µM ACh
in CM cells (n = 8). This response was decreased <95%
by 0.01 µM 4-diphenylacetoxy-N-methylpiperidine, a
M1/M3-selective antagonist, whereas 0.1 µM
methoctramine, a M2/M4-selective antagonist,
and 0.1 µM pirenzepine, a M1-selective antagonist, had
more modest effects. LM and CM cells showed similar results. We
conclude that human smooth muscle cells in primary culture express five
muscarinic receptor subtypes and respond to ACh with a rise in
[Ca2+]i mediated primarily by the
M3 receptor and involving release of Ca2+ from
intracellular stores. This culture model provides a useful tool for
further study of esophageal physiology.
calcium; signaling; antibodies; reverse transcriptase-polymerase chain reaction; immunocytochemistry; Western blotting
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