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 sho
wed, when exposed to a high extracellular [Ca2+], ([Ca2+](e)) a transient i
ncrease 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 (preexposure to high Ca2+). The maximum ch
arge movements in myoballs incubated in 1.8 and 4.8 mM were 16.4+/-1.05 (n=
56) and 24.1+/-1.18 nC/mu F (n=58; P<0.01), respectively, and peak Ca2+ cur
rents at 20 mV were -10.8+/-1.09 (n=46) and -12.8+/-0.75 nA/mu F (n=82), re
spectively (P>0.05). The tail current amplitudes in 1.8 and 4.8 mM Ca2+-tre
ated cells were -9.3+/-1.23 and -14.2+/-1.37 nA/mu F (P<0.05), respectively
, at 10 mV and -15.3+/-1.76 and -23.6+/-2.02 nA/mu F (P<0.05), respectively
at 60 mV. The maximum binding of [H-3]PN200-110 (a radioligand specific fo
r L-type Ca2+ channel alpha(1) 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 alpha
(1) subunits in skeletal muscle cells cultured in high [Ca2+](e) support th
e concept that extracellular Ca2+ influx modulates the expression of L-type
Ca2+ channels in skeletal muscle cells.