A Secondary Bio-Electric Effect of Potassium

Abstract

The usually large bio-electric effect of potassium salts is often ascribed to the high mobility of K⁺ ion in the protoplasmic surface It sometimes appears to be more complex, however, involving the mobility effect as an initial stage, with a secondary effect due to the deeper penetration of potassium. The two steps are often fused into an almost continuous curve in Nitella, but are more clearly distinguished in the closely related Chara coronata. In the cells of this plant the initial effects of KCl and NaCl are almost identical. The P. D. across 1 the protoplasm (100 to 150 mv. outside positive) is quickly reduced 40 or 50 mv. when tap water is replaced by 0.01 M NaCl or KCl, and then remains at this level for some time. During this time the polarization response remains about as quick and as large as in tap water, so that the effective resistance is high (e. g., 250,000 ohms) to small direct currents passing in either direction across the protoplasm. If an outward current be increased beyond the threshold of stimulation, or if an action current occurs spontaneously, the P. D. quickly falls to about zero. The polarization response also disappears, so that the resistance is entirely ohmic and very low (20,000 ohms).

Up to this point the effects of NaCl and KCl are almost identical. In the presence of NaCl recovery begins within a second or 2 and is completed in 5 to 30 seconds, with restoration of the normal P. D. and polarizability. But in the presence of KCl no such recovery occurs: the P. D. remains at about zero and polarization is absent even for rather large currents.

The secondary potassium effect is therefore the inhibition of recovery after an action current.