Ca2+ current enhancement by alpha 2/delta and beta subunits in Xenopus oocytes: contribution of changes in channel gating and alpha 1 protein level.
1. A combined biochemical and electrophysiological approach was used to determine the mechanism by which the auxiliary subunits of Ca2+ channel enhance the macroscopic Ca2+ currents. Xenopus oocytes were injected with RNA of the main pore-forming subunit (cardiac: alpha 1C), and various combinations of RNAs of the auxiliary subunits (alpha 2/delta and beta 2A). 2. The single channel open probability (Po; measured at 0 mV) was increased approximately 3-, approximately 8- and approximately 35-fold by alpha 2/delta, beta 2A and alpha 2/delta+beta 2A, respectively. The whole-cell Ca2+ channel current was increased approximately 8- to 10-fold by either alpha 2/delta or beta 2A, and synergistically > 100-fold by alpha 2/delta+beta 2A. The amount of 35S-labelled alpha 1 protein in the plasma membrane was not changed by coexpression of beta 2A, but was tripled by coexpression of alpha 2/delta (either with or without beta). 3. We conclude that the increase in macroscopic current by alpha 2/delta is equally due to changes in amount of alpha 1 in the plasma membrane and an increase in Po, whereas all of the effect of beta 2A is due to an increase in Po. The synergy between alpha 2/delta and beta in increasing the macroscopic current is due mainly to synergistic changes in channel gating.
Shistik
E
E
Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Israel.
Ivanina
T
T
Puri
T
T
Hosey
M
M
Dascal
N
N
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D004586:Electrophoresis; D007473:Ion Channels / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008565:Membrane Proteins / Q000502:physiology*; D009865:Oocytes / Q000502:physiology; D018408:Patch-Clamp Techniques; D014981:Xenopus
D015220:Calcium Channels; D007473:Ion Channels; D008565:Membrane Proteins; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester