THE IONIC REQUIREMENTS OF TRANSEPITHELIAL POTENTIALS IN HYDRA

¹ Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio 44106
² The Department of Biology, Case Western Reserve University, Cleveland, Ohio 44106

(1) The resting potential across the body wall of hydra varies monotonically with the external sodium concentration.

(2) Replacing bicarbonate and chloride, the normal external anions, with methane sulfonate changes the resting potential but not the transverse column impedance. If the anions are acting as passive shunts, the barrier across which the potential is developed must form but a small portion of the total transverse impedance.

(3) Changing the concentration of ions in the gut of hydra was generally without effect, but removal of calcium with EDTA caused the contraction pulses to become reduced or reversed in sign suggesting that these are calcium spikes.

(4) The resting potential changes in response to long term but not short term changes in the osmotic stress faced by the animal. It is proposed that the resting potential results from a sodium transport mechanism which is involved in osmotic regulation.

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