C-terminal modulatory domain controls coupling of voltage-sensing to pore opening in Cav1.3 L-type Ca(2+) channels.
Activity of voltage-gated Cav1.3 L-type Ca(2+) channels is required for proper hearing as well as sinoatrial node and brain function. This critically depends on their negative activation voltage range, which is further fine-tuned by alternative splicing. Shorter variants miss a C-terminal regulatory domain (CTM), which allows them to activate at even more negative potentials than C-terminally long-splice variants. It is at present unclear whether this is due to an increased voltage sensitivity of the Cav1.3 voltage-sensing domain, or an enhanced coupling of voltage-sensor conformational changes to the subsequent opening of the activation gate. We studied the voltage-dependence of voltage-sensor charge movement (QON-V) and of current activation (ICa-V) of the long (Cav1.3L) and a short Cav1.3 splice variant (Cav1.342A) expressed in tsA-201 cells using whole cell patch-clamp. Charge movement (QON) of Cav1.3L displayed a much steeper voltage-dependence and a more negative half-maximal activation voltage than Cav1.2 and Cav3.1. However, a significantly higher fraction of the total charge had to move for activation of Cav1.3 half-maximal conductance (Cav1.3: 68%; Cav1.2: 52%; Cav3.1: 22%). This indicated a weaker coupling of Cav1.3 voltage-sensor charge movement to pore opening. However, the coupling efficiency was strengthened in the absence of the CTM in Cav1.342A, thereby shifting ICa-V by 7.2 mV to potentials that were more negative without changing QON-V. We independently show that the presence of intracellular organic cations (such as n-methyl-D-glucamine) induces a pronounced negative shift of QON-V and a more negative activation of ICa-V of all three channels. These findings illustrate that the voltage sensors of Cav1.3 channels respond more sensitively to depolarization than those of Cav1.2 or Cav3.1. Weak coupling of voltage sensing to pore opening is enhanced in the absence of the CTM, allowing short Cav1.342A splice variants to activate at lower voltages without affecting QON-V.
Pharmacology and Toxicology, Institute of Pharmacy, and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria. Electronic address: andreas.lieb@student.uibk.ac.at.
Andreas
A
Lieb
Pharmacology and Toxicology, Institute of Pharmacy, and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria.
Nadine
N
Ortner
Pharmacology and Toxicology, Institute of Pharmacy, and Center for Molecular Biosciences, University of Innsbruck, Innsbruck, Austria. Electronic address: joerg.striessnig@uibk.ac.at.
Jörg
J
Striessnig
D017398:Alternative Splicing; D000818:Animals; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics; D020746:Calcium Channels, L-Type / Q000737:chemistry* / Q000235:genetics; D002412:Cations / Q000737:chemistry; D002462:Cell Membrane / Q000737:chemistry; D004553:Electric Conductivity; D004560:Electricity; D057809:HEK293 Cells; D006801:Humans; D042541:Intracellular Space / Q000737:chemistry; D015640:Ion Channel Gating; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000737:chemistry; D017434:Protein Structure, Tertiary; D051381:Rats; D014162:Transfection
C472073:CACNA1D protein, human; D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D002412:Cations; D020033:Protein Isoforms; C093712:Cacna1d protein, rat