The effects of aging on inhibitory neuropeptide concentrations and intrinsic inhibitory innervation of circular muscle were investigated using normal descending colon obtained at surgery. Immunoreactive vasoactive intestinal peptide, peptide histidine-methionine, met5-enkephalin, neuropeptide Y, and somatostatin were extracted from specimens of muscularis externa (patient ages: 19-84 years) and measured by radioimmunoassay. Intracellular electrical activity was recorded from strips of circular muscle (patients ages: 49-84 years) using glass microelectrodes; inhibitory junction potentials were evoked by electrical field stimulation. There were no significant differences (t tests:P>0.05) between neuropeptide concentrations in patients<70 years old (N=28) compared to patients≥70 years old (N=12). However, the amplitude of inhibitory junction potentials declined with increasing patient age (r=-0.58, P=0.02, N=16), with no change in resting membrane potentials (r=0.22;P>0.05). The decline in amplitude in women (r=-0.68, P=0.03, N=9) preceded the decline in men (r=-0.62, P=0.10, N=7). Age-related decline in inhibitory junction potentials could be related to decreased: density of inhibitory nerves, release of inhibitory neurotransmitter, density of binding sites for inhibitory neurotransmitter on smooth muscle, or a combination thereof. Alternatively, this decline might represent a change in interaction of inhibitory neurotransmitter with the smooth muscle membrane, such as a change in coupling of binding site with the potassium channel, decreased number of potassium channels, or altered permeability of the potassium channel.
- age-related change
- human colon
- smooth muscle
- vasoactive intestinal peptide
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