Properties of a calcium- and voltage-activated potassium current in Helix pomatia neurons
Lux, H.D.; Hofmeier, G.
Pflugers Archiv European Journal of Physiology 394(1): 61-69
1982
ISSN/ISBN: 0031-6768 PMID: 6289253 Document Number: 194178
A Ca- and voltage-dependent current was the principal outward current in identified Helix neurons. The current depends on the presence of Ca2+ 0, with half maximal activation at 1 mM Ca2+ 0, and it saturates beyond about 5 mM. The current is termed IK(Ca) since the charge carried by it corresponds to the amount of K ions transferred from the cell interior, as determined from the increase in K+ concentration in the external volume with K+ liquid ion-exchanger microelectrodes. IK(Ca) is characterized by bell shaped isochronal I/V curves. The peaks of these curves move from +30 mV to .apprx. +70 mV with an increase of the time of measurement from 30-200 ms. IK(Ca) rise times have a minimum of 10-15 ms at low depolarization around 0 mV, but increase about exponentially with more positive potentials. A 10-fold decrease in Ca2+ 0 over the range of 30-0.3 mM also produces an increase in rise time, equivalent to a positive shift of potential by 20 mV. On repolarization of the membrane IK(Ca) disappears much faster than the intracellular accumulated Ca2+, with a time constant which is similar to the minimum activation time constant.