Contact irritability of muscle and K/Ca ratio

In his 1900 work on comparative physiology of the brain, Loeb treated the righting of the starfish as a choice between two causes. Either gravity turns the ventral side down, or contact irritability, which he also called stereotropism, drives the animal to press its ventral side against solid bodies.¹ He noted that the animals leave the horizontal floor of an aquarium and attach to the vertical sides, which showed that gravity was not the cause.¹ In a sea anemone, he found that the contact irritability of the foot did not change when the head or the greater oral part was amputated. The mechanism therefore lay in the foot itself, not in the ganglion cells of the oral disc.²

Loeb's 1906 book The Dynamics of Living Matter reports Zoethout's work on muscle. Zoethout reasoned that potassium increases the tone of the muscle and calcium inhibits that action. Precipitating the calcium salts might therefore cause contact irritability by destroying the normal balance between the two.³ Zoethout reported that the view held up. The contact reaction produced by sodium citrate increased when K-ions had been introduced into the muscle before or at the same time.⁴ Zoethout also interpreted an earlier result with potassium salts as showing that the Ca-ions of the muscle itself are liable to antagonize the shortening action of the K-ions.³

Zoethout concluded that contact irritability depends on a disturbance of the normal ratio of salts in the muscle, and noted that Loeb had suggested this earlier.⁵ Loeb conceded that the experiment does not explain why the contact reaction appears only when the muscle is taken out of the citrate solution. He also leaned toward a part for the sodium salts as well as potassium.⁵ He revised his older statement about Na and Ca to include K and Ca. He added that substituting any univalent cation for Ca in the muscle, or the reverse, may cause twitching.⁶

Loeb's 1912 book recalls Ringer's earlier finding that heart contractions made abnormal by some salt mixtures were made normal by adding the missing salt. Ringer concluded that potassium and calcium are antagonists, like heart poisons that Schmiedeberg had studied.⁷ Bayliss in 1915 summarised Ringer's frog heart work. An efficient saline to replace blood needs potassium and calcium salts as well as sodium chloride, and it is the cation that is necessary.⁸ Potassium and calcium fluxes also appear in recent work on bioelectric signalling in planarian regeneration.⁹