. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 312 MARTIN MACKLIN AND ROBERT K. JOSEPHSON (T recovery is rapid when normal solution is readmitted just as with the resting potential. The effects of EDTA perfusion were variable and with some animals the CP's became small but remained negative. One reasonable explanation for the \.iriability in CP response to EDTA perfusion is that only a very small amount of divalent cation is required at the CP generating locus, an amount so small that it is but ineffectively removed by EDTA chelation in the face of diffusion from surroun
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 312 MARTIN MACKLIN AND ROBERT K. JOSEPHSON (T recovery is rapid when normal solution is readmitted just as with the resting potential. The effects of EDTA perfusion were variable and with some animals the CP's became small but remained negative. One reasonable explanation for the \.iriability in CP response to EDTA perfusion is that only a very small amount of divalent cation is required at the CP generating locus, an amount so small that it is but ineffectively removed by EDTA chelation in the face of diffusion from surrounding tissue. (C.) Osmotic pressure-effects Earlier it was hypothesized that the resting potential of hydra is the result of ion accumulating mechanisms used in osmoregulation (Macklin, 1967; Josephson and Macklin, 1969). One might therefore expect the size of the resting potential to reflect the osmotic stress faced by the animal. This was examined by determin- ing the effects on transepithelial potentials of bathing media which were hyper- osmotic to the normal medium. Increasing the osmotic concentration of the bath- ing medium somewhat above that of normal solution reduces the osmotic gradient between the tissues of the animal and its environment. In the first set of experi- ments (short term tests) the osmotic gradient was altered for 10 minute periods; in the second set of experiments (long term tests) the animals were kept in a solu- tion with elevated osmotic concentration for two weeks before testing. In the first short term tests the osmotic concentration of the bathing medium was varied by adding sucrose to normal solution ( mosmol) to give calculated osmotic concentrations up to mosmol. Animals did not fare well when ex- posed for 10 minute periods to these solutions presented in random order; the rest- = Co FREE EDTA. sec NORMAL FIGURE 10. The effect on CP's of internal perfusion with Ca-free-EDTA. The animal was bathed in normal solution. Here the penwriter
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