Effects of Near Membrane Electric Fields on Receptor Binding and Ion Channel Entry

The exponential decay of mV membrane potentials over nanometer distances near membranes produces electric fields capable of dissociating any non-covalent molecular complex within 6–7 nm of the membrane, while having negligible effects on dipole orientation. Protein receptor binding sites are shielded from the dissociative effects, the molecular shielding constant determined to be 7 x 10-8 cm2/V. The electric field effects hydration stripping, and its effect on ion entry, have not received significant investigation compared with intrachannel studies. Using measurements of ion velocity in electric fields, we show that calcium ions will be stripped of water on the outside of cells, entering channels within 4 nm of the membrane. Ions emerge on the inside 12 nm from the membrane, being immediately rehydrated and unable to re-enter the channel, creating a thyrofluidic valve. Measurements of sodium mobility show that hydration stripping occurs at electric fields within 6–7 nm from the membrane. These results can explain how hydrated sodium ions do not enter potassium channels (entry points beyond 7 nm) while stripped sodium ions can enter sodium channels (entry points within 6 nm), while the larger and essentially non-hydrated potassium ions only enter the larger diameter potassium channels. The largely unstudied near membrane electric field appears to influence both receptor and channel behavior.