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Abriola 1
Katie Abriola
Kaitlyn Bingham
Bio 142/Section 005
17 March 2015
The Chronotropic and Inotropic Cardiac effects of Acetylcholine, Atropine, and Potassium
Results:
Table 1 displays the chronotropic and inotropic effects of the drugs Acetylcholine, Atropine, and
Potassium on the heart. The table is divided into expected versus observed effects of each drug.
Acetylcholine was expected to produce a negative(-) inotropic effect, but a positive(+) effect was
observed. The expected chronotrophic effect of acetylcholine was negative(-), but when the drug
was administered, there was no chronotrpic effect observed. The second drug tested was atropine.
Atropine was both expected and observed to have positive(+) inotropic effects on the heart.
Atropine was also expected to elicit a positive(+) chronotropic effect, but a negative(-) effect was
observed on the heart. Following acetylcholine and atropine, the inotropic and chronotropic effects
of potassium were tested. Potassium was expected to prompt a negative(-) inotropic effect, but
once the drug was applied to the heart, no effect was observed. Potassium was also expected to
produce a negative(-) chronotropic effect, which was supported by the negative(-) effect observed.
(Tomicek&Waters. Lab Manual 2015).
DRUG
Acetylcholine
Atropine
+
Potassium (K )
Table 1: Effect of drugs on frog heart
Inotropic
Chronotropic
Expected Observed
Expected
Observed
Negative
Positive
Negative
No Effect
(-)
(+)
(-)
Positive
(+)
Positive
(+)
Positive
(+)
Negative
(-)
Negative
(-)
No Effect
Negative
(-)
Negative
(-)
*The chronotrophic and inotropic effects of each drug were
observed by retrieving a baseline reading of the heart rinsed with
the Ringer’s solution then administering 1-3 drops of the drug
tested. Results were recorded and heart was rinsed with Ringer’s
solution.
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Discussion:
The Laboratory was divided into various groups, allowing data/results to be compared. Students
were also provided with an online document provided by the instructor, which outlines the
expected outcome of each drug and gives detailed explanations. While some results were consistent
with other laboratory groups and the online resource, others differed. There are several sources of
error, which may be responsible for the varying results. Prior to each “new” drug being
administered, the ringer’s solution was intended to thoroughly rinse the heart of any lingering drug.
Since both the drugs and ringer solution are clear liquid, it is difficult to decipher whether the drug
had been entirely rinsed from the heart. If the drug is not entirely rinsed, while another is being
applied, they may interact causing the results to greatly change. Another source of error may have
been the amount of drug applied to the heart. Administering an excessive amount of the tested drug
may also effect the observed results. (Tomicek&Waters, Lab Manual 2015). While potassium
produced the expected results, atropine and acetylcholine were much different than anticipated.
Upon comparing the results to other groups and referencing the online document, it became
evident that our data was not particularly strong. Reviewing the physiology behind why the drugs
should be eliciting a certain response made it evident that some errors occurred through the course
of the experiment. Since acetylcholine decreases the entry of calcium into cells, it causes myosin
and actin to interact less. Ach also increases how much potassium is leaving, which causes the ECF
becomes more positive, which decreases heart rate. This would cause acetylcholine to have
negative inotropic and chronotrophic effects on the heart. Where acetylcholine should result in a
negative effect on the heart, atropine should be observed to have both positive inotropic and
chronotropic effects on the heart. This is due to atropine blocking acetylcholine receptors. This
causes a reverse of acetylcholine. (Tomicek&Waters,Powerpoint Presentation 2015).
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References
Tomicek, N. and Waters, J. “Cardiac Activity” Powerpoint Presentation. Pennsylvania State
University, Biology 142. 2015.
Tomicek, N. and Waters, J. “Physiology Laboratory Manual, Second Addition” Lab Manual.
Pennsylvania State University, Biology 142. 2015. Pp. 45-51. Print.