Calcium regulates L-type Ca2+ channel expression in rat skeletal muscle cells.
Primary skeletal muscle cells were cultured in a normal- (1.8 mM) or high- (4.8 mM) Ca2+ culture medium to determine whether Ca2+ modulates the number of L-type Ca2+ channels. Skeletal myoballs cultured in a normal medium showed, when exposed to a high extracellular [Ca2+], ([Ca2+]e) a transient increase in intracellular [Ca2+] ([Ca2+]i) from a resting concentration of 60 to 160 nM. By day 3, however, when the experiments were made, [Ca2+]i no longer differed from control (pre-exposure to high Ca2+). The maximum charge movements in myoballs incubated in 1.8 and 4.8 mM were 16.4+/-1.05 (n=56) and 24.1+/-1.18 nC/microF (n=58; P<0.01), respectively, and peak Ca2+ currents at 20 mV were -10.8+/-1.09 (n=46) and -12.8+/-0.75 nA/microF (n=82), respectively (P>0.05). The tail current amplitudes in 1.8 and 4.8 mM Ca2+-treated cells were -9.3+/-1.23 and -14.2+/-1.37 nA/microF (P<0.05), respectively, at 10 mV and -15.3+/-1.76 and -23.6+/-2.02 nA/microF (P<0.05), respectively at 60 mV. The maximum binding of [3H]PN200-110 (a radioligand specific for L-type Ca2+ channel alpha1 subunits) in myoballs cultured in 1.8 and 4.8 mM [Ca2+]e was 1.34+/-0.23 and 3.2+/-0.63 pmol/mg protein (n=8; P<0.02), respectively. The increase in [Ca2+]i associated with the increases in charge movements, tail currents and the number of L-type Ca2+ channel alpha1 subunits in skeletal muscle cells cultured in high [Ca2+]e support the concept that extracellular Ca2+ influx modulates the expression of L-type Ca2+ channels in skeletal muscle cells.
Renganathan
M
M
Department of Internal Medicine, Gerontology, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, USA.
Wang
Z M
ZM
Messi
M L
ML
Delbono
O
O
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000378:metabolism; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000502:physiology*; D002478:Cells, Cultured; D004553:Electric Conductivity; D017275:Isradipine / Q000378:metabolism; D008564:Membrane Potentials; D018482:Muscle, Skeletal / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D002118:Calcium; D017275:Isradipine