Properties of two types of calcium channels in clonal pituitary cells.
Open Access
- 1 January 1986
- journal article
- Published by Rockefeller University Press in The Journal of general physiology
- Vol. 87 (1), 161-182
- https://doi.org/10.1085/jgp.87.1.161
Abstract
The calcium currents of GH3 cells have been studied using the whole cell variant of the patch-clamp technique. Under conditions that eliminate sodium and potassium currents, we observed inward currents that activated within a few milliseconds, and deactivated with two time constants, approximately 150 microseconds and 3 ms at -80 mV, 18-20 degrees C. The components are called FD and SD (fast deactivating and slow deactivating). Both components are calcium currents, and are greatly reduced when magnesium is substituted for most of the calcium in the bath. In addition to (a) their different rates of deactivation, the two components differ in a number of other properties. (b) The SD component inactivates almost completely, with a time constant of 23 ms at 20 mV, 19 degrees C. The FD component, on the other hand, shows little or no sign of inactivation, and is almost the same in amplitude from 10 to 100 ms. The components thus seem quite independent of each other, and must arise from two independent sets of channels. (c) The FD channels activate more rapidly than SD at 20 mV, by a factor of approximately 2 as is shown in several ways. (d) In 10 Ca or 10 Ba, the activation curve for SD channels is approximately 20 mV more negative than for FD or Na channels. (e) FD channels conduct barium ions more effectively than calcium by a ratio of approximately 2. (f) FD channels "wash out" within minutes after the patch electrode breaks into a cell, whereas SD channel current remains relatively stable. It is argued that SD channels, because of their negative activation threshold, are involved in electrical events near threshold, and that FD channels are best suited for calcium injection once a spike has been initiated.Keywords
This publication has 16 references indexed in Scilit:
- Two types of calcium channels in the somatic membrane of new‐born rat dorsal root ganglion neurones.The Journal of Physiology, 1985
- Threshold channels—a novel type of sodium channel in squid giant axonNature, 1984
- Na and Ca channels in a transformed line of anterior pituitary cells.The Journal of general physiology, 1984
- Sodium and calcium channels in bovine chromaffin cellsThe Journal of Physiology, 1982
- Potassium current suppression by quinidine reveals additional calcium currents in neuroblastoma cells.Proceedings of the National Academy of Sciences of the United States of America, 1981
- Improved patch-clamp techniques for high-resolution current recording from cells and cell-free membrane patchesPflügers Archiv - European Journal of Physiology, 1981
- Electrophysiology of mammalian inferior olivary neurones in vitro. Different types of voltage‐dependent ionic conductances.The Journal of Physiology, 1981
- Calcium ChannelAnnual Review of Neuroscience, 1981
- Calcium Entry Leads to Inactivation of Calcium Channel in ParameciumScience, 1978
- Charge Movement Associated with the Opening and Closing of the Activation Gates of the Na ChannelsThe Journal of general physiology, 1974