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Cobalt‐Dependent potentiation of net inward current density in Helix aspersa neurons
Author(s) -
Kim YK.,
Woodruff M. L.
Publication year - 1991
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.490280411
Subject(s) - tetraethylammonium , depolarization , chemistry , biophysics , potassium , biology , organic chemistry
A low concentration of transition metal ions Co 2+ and Ni 2+ increases the inward current density in neurons from the land snail Helix aspersa . The currents were measured using a single electrode voltage‐clamp/internal perfusion method under conditions in which the external Na + was replaced by Tris + the predominant external current carrying cation was Ca 2+ and the internal perfusate contained 120 mM Cs + /0 K + ; 30 mM tetraethylammonium (TEA) was addedexternally to block K + carrent. In presence of Co 2+ (3 mM) Ni 2+ Ca 2+ currents were stimulated normally by voltage‐dependent activation of Ca 2+ channels. There was a 5‐10% decrease in the rate of rise of the inward current The principal effect of Co 2+ and Ni 2+ current density seems to be a decrease in the rate at which the inward currents decline during a depolarizing voltage pulse. The results may be due to a decrease in a voltage‐dependent or Ca 2+ ‐dependent outward current and/or an inhibition of Ca 2+ channel inactivation. Outward current under these conditions (zero internal K + ) was significant and most likely due to Cs + efflux through the voltage activated or Ca 2+ ‐activated nonspecification channels. Co 2+ is an extremely effective blocker of this outward current. These results are not an artifact of internal perfusion or the special ionic conditions. Intracellular recording of unperfused neurons in normal Helix Ringer solution showed that the Ca 2+ ‐dependent action potential duration was increased significantly by low concentrations of Co 2+ . This result is consistant with the Co 2+ ‐dependent increase in inward (depolarizing) current seen in voltage‐clamp experiments.