Abstract
A mathematical model for the periodic electrical activity of a functional unit of the small intestine is developed. Based on real morphological and electrophysiological data, the model assumes that: the functional unit is an electromyogenic syncytium; the kinetics of L, T-type Ca2+, mixed Ca2+-dependent K+, potential sensitive K+ and Cl− channels determines electrical activity of the functional unit; the basic neural circuit, represented by a single cholinergic neurone, provides an excitatory input to the functional unit via receptor-linked L-type Ca2+ channels. Numerical simulation of the model has shown that it is capable of displaying the slow waves and that slight modifications of some of the parameters result in different electrical responses. The effects of the variations of the main parameters have been analyzed for their ability to reproduce various electrical patterns. The results are in good qualitative and quantitative agreement with results of experiments conducted on the small intestine.
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Abbreviations
- C am :
-
capacitance of the nerve fiber
- C p :
-
subsynaptic membrane capacitance
- C m :
-
membrane capacitance (smooth muscle, SM)
- R a :
-
membrane resistance (nerve fibre, NF)
- R v :
-
resistance of the extrasynaptic structures
- ϕ :
-
membrane potential (SM)
- ϕ * :
-
membrane potential (NF)
- ϕ p :
-
excitatory postsynaptic potential
- ϕ rest :
-
resting potential (SM)
- ϕ Na, ϕ K, ϕ Cl :
-
reversal potentials for Na+, K+ and Cl− currents (NF)
- \(\tilde \varphi {\text{Ca}}\) :
-
reversal potential for fast Ca2+ current (SM)
- \(\tilde \varphi {\text{K}}\) :
-
reversal potential for slow K+ current (SM)
- \(\tilde \varphi {\text{Cl}}\) :
-
reversal potential for slow Cl− current (SM)
- \(\tilde \varphi {\text{Ca}}\) :
-
calcium equilibrium potential (SM)
- ϕ R :
-
resting potential of the synapse
- ϕ o :
-
excitatory potential
- ϕ *p :
-
threshold potential for L-type Ca2+ channels
- g Na, g K, g Cl :
-
maximal conductances for Na+, K+ and Cl− currents (NF)
- \(\tilde g_{{\text{Ca}}}^{\text{f}} ,{\text{ }}\tilde g_{{\text{Ca}}}^{\text{s}} \) :
-
maximal conductance of fast and slow Ca2+ channels, respectively (SM)
- \(\tilde g{\text{K, }}\tilde g{\text{Ca - K}}\) :
-
maximal conductance of K+ and Ca2+ activated
- K+ :
-
channels (SM)
- \(\tilde g{\text{Cl}}\) :
-
maximal conductance of leak Cl− channels (SM)
- m :
-
activation gating variable of Na+ current (NF)
- h :
-
inactivation gating variable of Na+ current (NF)
- \(\tilde m_I \) :
-
steady-state of activation gating variable of fast Ca2+ current (SM)
- \(\tilde h\) :
-
inactivation gating variable of fast Ca2+ current (SM)
- ñ :
-
activation gating variable of fast K+ current (SM)
- αm, h, n :
-
activation time constants of Na+ and K+ channels (NF)
- β m, h, n :
-
deactivation time constants of Na+ and K+ channels (NF)
- \(\tilde \alpha _{{\text{m,h,n}}} \) :
-
activation time constants of fast Ca2+ and K+ channels (SM)
- \(\tilde \beta _{{\text{m,h,n}}} \) :
-
deactivation time constants of fast Ca2+ and K+ channels (SM)
- I fCa , I SCa :
-
fast and slow Ca2+ currents, respectively (SM)
- I K :
-
potential sensitive K+ current (SM)
- I lC :
-
leak current (SM)
- ACh:
-
acetylcholine
- AChc :
-
fraction of acetylcholine in the cleft
- AChv :
-
vesicular acetylcholine
- AChf :
-
free fraction of acetylcholine
- AChp :
-
postsynaptic fraction of acetylcholine
- R:
-
choline receptors
- ACh-R:
-
acetylcholine-receptor complex
- E:
-
acetylcholinesterase enzyme
- AChE:
-
acetylcholine-enzyme complex
- S:
-
products of chemical reactions
- [...]:
-
concentration of the reacting components
- [Ca2+]out :
-
external calcium concentration (synapse)
- [Ca2+]:
-
internal calcium concentration (synapse)
- \(\tilde Ca^{2 + } \) :
-
internal calcium concentration (SM)
- k c :
-
affinity constant (synapse)
- k d :
-
diffusion constant (synapse)
- k + p :
-
diffusion velocity constant of acetylcholine on the subsynaptic membrane
- k +,- :
-
constants of forward (+) "and backward (−) chemical reactions (synapse)"
- a :
-
cross-section diameter of the axon
- L :
-
length of the axon
- L o :
-
length of the nerve terminal
- Ω :
-
empirical constant of synapse
- τx ca :
-
relaxation time constant of Ca2+ current (SM)
- \(\tilde x_{{\text{ca}}} \) :
-
relaxation parameter for activation of intracellular Ca2+ current (SM)
- α:
-
numerical parameter
- λ :
-
Plant's factor
- ϱ :
-
strength of the cellular Ca2+ buffering capacity (SM)
- K c :
-
intracellular Ca2+ current constant (SM)
- t :
-
time
- t s :
-
time of excitation
- s :
-
Lagrangian coordinate
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Miftakhov, R.N., Abdusheva, G.R. & Wingate, D.L. Model predictions of myoelectrical activity of the small bowel. Biol. Cybern. 74, 167–179 (1996). https://doi.org/10.1007/BF00204205
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DOI: https://doi.org/10.1007/BF00204205