Skeletal muscle L-type Ca(2+) current modulation in gamma1-deficient and wildtype murine myotubes by the gamma1 subunit and cAMP.
Modulation of the steady-state inactivation and current amplitude by the gamma1 subunit of the murine skeletal muscle L-type Ca(2+) channel were investigated using the whole-cell patch-clamp technique. Transient expression of the gamma1 subunit, but not of the gamma2 (stargazin) protein, in primary cultured myotubes from gamma1-deficient mice shifted the steady-state inactivation approximately -15 mV, thereby restoring wildtype (WT) steady-state inactivation and current amplitude. The increased Ca(2+) current amplitude in gamma1-deficient cells was abolished in myotubes from animals of 4 weeks and older whereas the positive shift in steady-state inactivation was independent of mouse age. Raising intracellular cAMP levels using the membrane-permeant analogue 8-Br-cAMP led to an increase in Ca(2+) current amplitude in WT cells to the level in gamma1-deficient myotubes. There was no effect on the current amplitude in gamma1-deficient cells or on the steady-state inactivation in either genotype. Rp-cAMPS, a competitive inhibitor of cAMP-dependent protein kinase, had no effect on the WT Ca(2+) current amplitude and steady-state inactivation, but diminished the current amplitude in gamma1-deficient myotubes without affecting the steady-state inactivation in these cells. These data show that the increased Ca(2+) influx in myotubes lacking the gamma1 subunit, due to right-shifted steady-state inactivation and increased L-type Ca(2+) current amplitude, is determined by the gamma1 subunit. The effect on current amplitude depends on the age of the mice and its cAMP-dependent modulation appears to be controlled by the gamma1 subunit.
Held
Brigitte
B
Institut für Experimentelle und Klinische Pharmakologie & Toxikologie, Universität des Saarlandes, 66421 Homburg/Saar, Germany. brigette.held@uniklinik-saarland.de
Freise
Doris
D
Freichel
Marc
M
Hoth
Markus
M
Flockerzi
Veit
V
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000375:Aging / Q000502:physiology; D000465:Algorithms; D000818:Animals; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology / Q000502:physiology*; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004594:Electrophysiology; D051379:Mice; D008870:Microtubules / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D018408:Patch-Clamp Techniques; D013873:Thionucleotides / Q000494:pharmacology; D014162:Transfection
D020746:Calcium Channels, L-Type; D013873:Thionucleotides; D015124:8-Bromo Cyclic Adenosine Monophosphate; C016957:adenosine-3',5'-cyclic phosphorothioate; D004247:DNA; D000242:Cyclic AMP