Two Distinct Populations of Calcium Channels in a Clonal Line of Pituitary Cells

The whole-cell variant of the patch clamp technique was used to study calcium channels in GH3 cells. Two distinct populations of calcium channels, first recognized from their closing kinetics, were observed. The slowly closing channels are activated in a relatively negative voltage range and are inactivated within 100 milliseconds. They conduct barium and calcium about equally well. The fast closing channels are activated at more positive voltages, are not inactivated during a 100-millisecond pulse, conduct barium in preference to calcium, and are activated slightly more rapidly than the slowly closing channels.