Currents carried by monovalent cations through calcium channels in mouse neoplastic B lymphocytes.

Abstract

SUMMARY1. Membrane currents through the Ca2+ channel were studied in a hybridoma cell line (MAb-7B) constructed by fusion ofSI94 myeloma cells and splenic B lymphocytes from the mouse. The whole-cell variation of the patch-electrode voltage-clamp technique was used. 3. Both inward and outward currents showed voltage-dependent inactivation with the same membrane potential dependence of steady-state inactivation.4. The decay time constant of the current decreased from about 27 ms at -44 mV to a saturation value of 16 ms at about -20 mV, and remained at this value even when the current became outward.5. From the above results both the inward and outward currents were considered to flow through Ca2+ channels. Y. FUKUSHIMA AND S. HAGIWARA 11. The suppression of the monovalent currents by Ca2+ and Mg2+ showed different voltage dependences. The suppression by Ca2+ increased and then decreased as the membrane potential was made negative, whereas the suppression by Mg2+ increased monotonically. This difference can be explained by considering the fact that Ca2+ is permeant and Mg2+ is impermeant through the Ca2+ channel.12. Under certain conditions the Ca2+ inward current coexisted with the monovalent inward current.13. The selectivity of the Ca2+ channel for monovalent cations in media containing low concentrations of divalent cations was evaluated from the reversal potential. Permeability ratios calculated were 1-0 for Na+, 0-8 for K+, 0-6 for Rb+ and 035 for Cs+. The ability of monovalent cations to carry the outward current at large positive potentials showed the same sequence.

Mouse sperm membrane potential: changes induced by Ca2+

“…4A suggests that both divalent ions permeate through the same channel, Ca 2+ passes more efficiently and Mg 2+ blocks. This is consistent with the properties of other Ca 2+ channels [14,25]. The Ca-id was blocked with TFP and NDP (Fig.…”

“…This Ca-ith strongly depended on [Na+]e. When [Na+]e was replaced by a non-permeant monovalent cation, the Ca-ith decreased and completely disappeared at around 40 mM [Na+]e. These results suggest that in the absence of Ca -'+, Na ÷ can permeate through Ca 2+ channels, as is the case in other systems [14,25]. On the other hand, ouabain, a specific inhibitor of the Na-K ATPase, inhibited 70% of the Ca-ith, indicating the participation of this pump in the response.…”

Depletion of intracellular calcium stores activates an outward potassium current in mast and RBL‐1 cells that is correlated with CRAC channel activation

“…Better permeation of K + and Na + compared to Cs + in the presence of external divalent cations was also reported for various VOC channels [10,12]. However, CRAC channels behave differently from VOC channels in terms of monovalent permeation in the following ways.…”

“…(1) Outward Cs + currents through VOC channels have been measured in different cell types [8,10,12,18] whereas CRAC channels seemed not to carry any Cs + current. (2) Only the removal of external Ca 2+ was necessary to obtain huge monovalent currents through VOC channels [10,12] whereas all divalent cations (including Mg 2+) had to be removed to allow large monovalent inward currents through CRAC channels [14,19].…”

Molecular Physiology of Low-Voltage-Activated T-type Calcium Channels

“…An effect called surface charge screening. Increasing external [Ca 2ϩ ] from 2 to 10 mM shifts the apparent gating of T-type channels by ϳ10 mV (128).…”