. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 304 M \RTIN 'KLIN AND ROBERT K. JOSEPHSON olution tended to increase the resting- potential of internally perfused animals above that of animals which were not so perfused. Third, the resting potential lends to increase for some time after the animal is mounted on the test holder, and so the initial resting potential is somewhat arbitrary. Since the increase was most pronounced for the first fifteen minutes, and since in the previous work we had started the measurement of the resting potential sooner than in these experi-
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 304 M \RTIN 'KLIN AND ROBERT K. JOSEPHSON olution tended to increase the resting- potential of internally perfused animals above that of animals which were not so perfused. Third, the resting potential lends to increase for some time after the animal is mounted on the test holder, and so the initial resting potential is somewhat arbitrary. Since the increase was most pronounced for the first fifteen minutes, and since in the previous work we had started the measurement of the resting potential sooner than in these experi- ments, the increase in reported resting potential is due in part to the experimental protocol followed. (A). External ion substitution (1). External cation substitution—sodium. Sodium was replaced by either potassium or tris ion to determine its effect on the hydra transepithelial resting potential and the contraction pulse. The results with the two substituting ions were similar but not identical. Removing sodium in both cases caused the resting potential to fall. For three animals the average potential in normal solution was 67 mv (range 61 to 75) and in sodium-free potassium solution it was mv (range -—k4 to ). Similarily for three other animals the average resting po- tential in normal solution was 63 mv (range 52 to 77) and in sodium free tris solution it was -19 mv (range —26 to -10). These resting potentials were measured for the last five minutes of ten minute test periods as described above; two to five test sequences were done with each animal. The results show that maintenance of the potential requires sodium in the external medium and neither potassium nor tris will substitute. The changes in the resting potential at the onset of perfusion with sodium-free solution and at the readmission of solution containing sodium are not symmetrical; the latter is much more abrupt (Figs. 2, 3 and 4). This suggests that the relation Z LU I— o Q_ 80 40 0 J 20 No FR
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
