The sensitivity of Helix aspersa neurones to injected calcium ions.
1. When calcium chloride was injected into Helix aspersa neurones there was a fall in membrane resistance and the membrane potential became hyperpolarized.2. The reversal potential of the response was dependent on the concentration of potassium in the external solution.3. Injection of a calcium-EGTA buffer containing 9 x 10(-7)M free calcium reduced the membrane resistance by 25%. When calcium chloride was injected it was necessary to increase the total intracellular calcium concentration by about 10(-3)M to produce similar change of resistance.4. In sodium-free (Tris) solution there was a slow fall of membrane resistance as if the intracellular calcium concentration had increased. There was a similar resistance change in the presence of 2,4-dinitrophenol and iodoacetate.5. A series of repetitive depolarizing pulses produced a long lasting reduction in membrane resistance which was enhanced by 2,4-dinitrophenol and iodoacetate.6. It is concluded that (a) injection of calcium causes an increase in potassium permeability, (b) the injected calcium is rapidly pumped from the cytoplasm by a sodium-dependent mechanism and by mitochondria, and (c) 1-2 msec depolarizing pulses stimulate an influx of calcium. This influx is rapid enough to trigger potassium activation during an action potential.
D000200:Action Potentials; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002021:Buffers; D002118:Calcium / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D004140:Dinitrophenols / Q000494:pharmacology; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007461:Iodoacetates / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects*; D009474:Neurons / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology; D012908:Snails / Q000502:physiology*
D002021:Buffers; D004140:Dinitrophenols; D007461:Iodoacetates; D011188:Potassium; D002118:Calcium