Suxamethonium 8 μM(muscle direct stimulation) Neostigmine 0.2 μM (muscle direct stimulation)
+Wash
Table 12: Injection of SUX and NEO in nerve and muscle at different doses.
Discussion:
Part I - Cholinergic transmission at the neuromuscular junction
16
, TUB: When stimulated in the nerve in the experiment it will result in blocked depolarization, we can observe
this in table 1, where the electrical impulses flat lines for both dose 5 mcg and 25 mcg. TUB is competitively
binding to the nicotinic receptor post synaptically and blocks ACh from even binding, it is an antagonist. We
say that this results in a non-depolarizing block (it prevents the motor endplate from depolarizing). When
stimulated in the muscle we observe no effect on the electrical impulses, because within the muscle fiber there
are no nicotinic receptors for the drug to bind to, because they are found post synaptically in the membrane
(acetylcholine receptor AChR). So to sum up the most important locations of the nicotinic acetylcholine
receptors: they are found at the neuromuscular junction of the skeletal muscle, autonomic ganglia and adrenal
medulla (Pakala and Brown, 2020).
TTX: Voltage gated sodium channels are the target for TTX and they are expressed in the neuromuscular
junction and within muscle fiber, so the effect of stimulating nerve indirectly and muscle directly can be
observed in table 2, where TTX has effect in both incidences. It binds to the voltage gated channel and inhibits
action potential. 0.2 mcg leads to a partial block while 2mcg leads to a full block to overcome the threshold for
the action potential to propagate. This is a drug that has a non-depolarizing block effect which results in
muscle paralysis (Pakala and Brown, 2020).
4-AP: Voltage gated potassium channels are the target for 4-AP, it binds to it as an antagonist which blocks it.
By blocking it at low dose it improves the axon's signal transduction keeping it positive longer, because the
channel would normally leak causing the action potential to stop. At table 3 in muscle and nerve stimulation we
can see at 5 mcg 4-AP injected we can observe this effect with an increase in the electrical impulses. Since it
has the opposite effect of non-depolarizing drugs it is used in anesthetics as a reversal agent for these drugs
(Kostadinova and Danchev, 2019)(Bostock, Sears and Sherratt, 1981).
NEO: inhibits acetylcholinesterase (AChE), this decreases the breakdown of acetylcholine (ACh), so the levels
of ACh increases in the synaptic cleft. Thereby increasing the ability to cause action potential (by increasing the
Na+ inside the neuron and opening voltage gated channels) and subsequent depolarization, since AChE can be
found in the synaptic cleft and not within muscle we see no response in stimulation of muscle in table 4, while a
response increase in electrical signaling by stimulation of nerve in the same table. This drug is used to
counteract the effects of non-depolarizing muscle relaxant by its mechanism causing depolarization.
ATR: Has its target mechanism (block muscarinic acetylcholine receptors) in skeletal muscle, therefore no effect
can be observed in table 5 in both stimulating smooth muscle directly and nerve indirectly respectively.
Part II -Neostigmine and tubocurarine in combination
17
+Wash
Table 12: Injection of SUX and NEO in nerve and muscle at different doses.
Discussion:
Part I - Cholinergic transmission at the neuromuscular junction
16
, TUB: When stimulated in the nerve in the experiment it will result in blocked depolarization, we can observe
this in table 1, where the electrical impulses flat lines for both dose 5 mcg and 25 mcg. TUB is competitively
binding to the nicotinic receptor post synaptically and blocks ACh from even binding, it is an antagonist. We
say that this results in a non-depolarizing block (it prevents the motor endplate from depolarizing). When
stimulated in the muscle we observe no effect on the electrical impulses, because within the muscle fiber there
are no nicotinic receptors for the drug to bind to, because they are found post synaptically in the membrane
(acetylcholine receptor AChR). So to sum up the most important locations of the nicotinic acetylcholine
receptors: they are found at the neuromuscular junction of the skeletal muscle, autonomic ganglia and adrenal
medulla (Pakala and Brown, 2020).
TTX: Voltage gated sodium channels are the target for TTX and they are expressed in the neuromuscular
junction and within muscle fiber, so the effect of stimulating nerve indirectly and muscle directly can be
observed in table 2, where TTX has effect in both incidences. It binds to the voltage gated channel and inhibits
action potential. 0.2 mcg leads to a partial block while 2mcg leads to a full block to overcome the threshold for
the action potential to propagate. This is a drug that has a non-depolarizing block effect which results in
muscle paralysis (Pakala and Brown, 2020).
4-AP: Voltage gated potassium channels are the target for 4-AP, it binds to it as an antagonist which blocks it.
By blocking it at low dose it improves the axon's signal transduction keeping it positive longer, because the
channel would normally leak causing the action potential to stop. At table 3 in muscle and nerve stimulation we
can see at 5 mcg 4-AP injected we can observe this effect with an increase in the electrical impulses. Since it
has the opposite effect of non-depolarizing drugs it is used in anesthetics as a reversal agent for these drugs
(Kostadinova and Danchev, 2019)(Bostock, Sears and Sherratt, 1981).
NEO: inhibits acetylcholinesterase (AChE), this decreases the breakdown of acetylcholine (ACh), so the levels
of ACh increases in the synaptic cleft. Thereby increasing the ability to cause action potential (by increasing the
Na+ inside the neuron and opening voltage gated channels) and subsequent depolarization, since AChE can be
found in the synaptic cleft and not within muscle we see no response in stimulation of muscle in table 4, while a
response increase in electrical signaling by stimulation of nerve in the same table. This drug is used to
counteract the effects of non-depolarizing muscle relaxant by its mechanism causing depolarization.
ATR: Has its target mechanism (block muscarinic acetylcholine receptors) in skeletal muscle, therefore no effect
can be observed in table 5 in both stimulating smooth muscle directly and nerve indirectly respectively.
Part II -Neostigmine and tubocurarine in combination
17
