T-type and N-type calcium channels of Xenopus oocytes: evidence for specific interactions with beta subunits.
We used amplifying effects of calcium channel beta subunits to identify endogenous calcium channels in Xenopus oocytes. Expression of rat brain beta 4 increased macroscopic endogenous current magnitude with a small effect on kinetics. In contrast, expression of rat brain/cardiac beta 2 produced a much larger increase in current magnitude and dramatically slowed current decay. Low concentrations of omega-conotoxin GVIA irreversibly blocked currents in both uninjected and beta 2-injected oocytes. Single channel recordings revealed both T- and N-type calcium channels with conductances of 9 and 18 pS, respectively, in uninjected oocytes and in oocytes expressing either beta subunit. Expression of either beta subunit slowed average current decay of T-type single channels. Slowing of T-type current decay by expression of beta 2 was due to reopening of the channels. N-type single channel average current decay showed little change with expression of beta 4, whereas expression of beta 2 slowed average current decay.
Lacerda
A E
AE
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030.
Perez-Reyes
E
E
Wei
X
X
Castellano
A
A
Brown
A M
AM
D000818:Animals; D001921:Brain / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000096:biosynthesis / Q000737:chemistry / Q000502:physiology*; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D005260:Female; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D008978:Mollusk Venoms / Q000494:pharmacology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D014982:Xenopus laevis; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D046911:Macromolecular Substances; D008978:Mollusk Venoms; D010455:Peptides; D020866:omega-Conotoxin GVIA