Absence of regulation of the T-type calcium current by Cav1.1, beta1a and gamma1 dihydropyridine receptor subunits in skeletal muscle cells.
The subunit structure of low voltage activated T-type Ca2+ channels is still unknown. Co-expression of dihydropyridine receptor (DHPR) auxiliary subunits with T-type alpha1 subunits in heterologous systems has produced conflicting results. In developing foetal skeletal muscle fibres which abundantly express DHPR subunits, Cav3.2 (alpha1H) subunits are believed to underlie T-type calcium currents which disappear 2 to 3 weeks after birth. Therefore, a possible regulation of foetal skeletal muscle T-type Ca2+ channels by DHPR subunits was investigated in freshly isolated foetal skeletal muscle using knockout mice, which provide a powerful tool to address this question. The possible involvement of alpha1S (Cav1.1), beta1 and gamma1 DHPR subunits was tested using dysgenic (alpha1S-null), beta1a and gamma1 knockout mice. The results show that the absence of alpha1S, beta1 or gamma1 DHPR subunits does not significantly affect the electrophysiological properties of T-type Ca2+ currents in skeletal muscle, suggesting that (1) native Cav3.2 is not regulated by beta1 or gamma1 DHPR subunits; (2) T-type and L-type currents have distinct and not interchangeable roles.
Strube
Caroline
C
UMR CNRS 5123, UCB-Lyon1, 69622, Villeurbanne, Cedex, France. caroline.strube@univmed.fr
D000818:Animals; D002118:Calcium / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000235:genetics / Q000502:physiology*; D020747:Calcium Channels, T-Type / Q000235:genetics / Q000502:physiology*; D005260:Female; D051379:Mice; D018345:Mice, Knockout; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D021122:Protein Subunits / Q000235:genetics / Q000502:physiology*
C529218:CACNA1S protein, mouse; C504883:Cacna1h protein, mouse; C492923:Cacnb1 protein, mouse; D020746:Calcium Channels, L-Type; D020747:Calcium Channels, T-Type; D021122:Protein Subunits; D002118:Calcium