Potassium occurs in large amounts in the earth crust, while in seawater and in living
organisms exclusively in the form of potassium compounds. With an average molar concentration of
1,02.10-2 mol/l (expressed in mass units: 399 mg/l) potassium is the eighth most abundant
element in seawater.
Version 2012-III
Potassium - (Kalium ) - K
Potassium occurs
in large amounts in the earth crust, while in seawater and in living
organisms exclusively in the form of potassium compounds. With an
average molar concentration of 1,02.10-2 mol/l (expressed in mass
units: 399 mg/l) potassium is the eighth most abundant element in seawater.
Occurrence
Potassium occurs in marine water exclusively in the form of its cation
K+.
Biogenous role
Potassium is a known biogenous element whose proper function in biologic
processes depends on its absolute concentration, as well as to a certain
extent on the relation of its concentration to that of other elements,
e.g. sodium (Na) and calcium (Ca).
The influence of potassium, sodium
and calcium on muscle tissue contraction – more specifically the efficiency
thereof - was studied on crustaceans in a series of experiments. A live
muscle tissue probe of the Opisthobranch aplysia punctata was suspended
in a series of solutions with different compositions in the order listed
below and the following observations were made regarding the tissue muscle
contraction:
K + Ca + Na
Normal rhythmic activity
Ca + Na
Strong irregular contraction
Na:
Further contraction amplification, random occurrence of fast smaller
amplitude contractions
Ca + Na:
Partial relief, frequency of the occurring sporadic contractions
decreases
K + Ca + Na:
Complete reversion to the original status - normal rhythmic activity
The experiment described above proves that potassium increases the
frequency and the amplitude of contraction tissue, while calcium decreases
it. The negative calcium effect is not as strong as the positive potassium
effect, which means that calcium abundance has no negative effect on
muscle contraction, if otherwise the composition – and primarily the potassium
concentration - is right. Further experiments showed that potassium abundance
has a similar effect as potassium deficiency, and that certain trace
elements have a similar effect on muscle tissue as potassium.
Further experiments were carried out to study the effect of potassium
on the activity of the enzyme phosphofructokinase, which plays a key
role in carbohydrate catabolism (also known as glycolysis), and in this
manner also in energy supply for live organisms.
The diagram at the beginning of this contribution shows, that even a
small potassium concentration decrease causes a decrease in the activity
of phosphofructokinase:
Phosphofructokinase activity decrease
=
Slowdown of glycolysis
=
Slowdown of energy transfer to the cells
Summary
Occurrence in seawater:
Potassium cation K+
Recommended concentration:
400 mg/l (390 – 410 mg/l)
Influence on:
Invertebrates
Biogenous role:
Muscle tissue efficiency, carbohydrate metabolism
Literature
MThe Effects of Ammonium, Inorganic Phosphate and Potassium Ions on the Activity of Phosphofructokinases from Muscle and Nervous Tissues of Vertebrates and Invertebrates. By P. H. SUGDEN* and E. A. NEWSHOLMET A.R.C. Unit of Muscle Mechanisms and Insect Physiology, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, U.K. (16 April 1975) THE ACTION OF POTASSIUM ON MUSCLEPREPARATIONS FROM INVERTEBRATES BY GEORGE P. WELLS. From the Laboratory of the Marine Biological Association, Plymouth, and the Department of Physiology and Biochemistry, University College, London. (8th December 1927)
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