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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.


Version 2012-III

Potassium - (Kalium ) - K

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:

 
Graph

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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