Table 1.

Role of calcium in NT-3 gene expression in embryonic muscle cells

Ca2+ionophores
Control	A23187 3 μm	Ionomycin 3 μm
1.00  ± 0.03	1.64  ± 0.03*	1.81  ± 0.01*
Ca2+-free media
Control	K+ 35 mm	Control	Veratridine 10 μm
1.00  ± 0.02	0.97  ± 0.10	1.00  ± 0.05	0.67  ± 0.13
Cd2+media
Control	K+ 35 mm	Control	Veratridine 10 μm
1.00  ± 0.07	0.96  ± 0.03	1.00  ± 0.07	0.84  ± 0.09
L-type channels
Control	Veratridine 10 μm	Veratridine 10 μm	Veratridine 10 μm	Veratridine 10 μm
		+ nitrendipine 10 μm	+ nifedipine 10 μm	+ verapamil 10 μm
1.00  ± 0.02	2.69  ± 0.08*	2.31  ± 0.21*	1.84  ± 0.13*	1.65  ± 0.12*

Xenopus muscle cells were cultured for 3 d and then treated with the indicated drugs for 1 hr at the indicated concentrations. “Control” means the group with no drug treatment. To prevent Ca²⁺ influx into the muscle cells, we first replaced culture media by Ca²⁺-free media (Ringer’s solution that contains no Ca²⁺) or Cd²⁺ media (Ringer’s solution that contains 0.1 mmCdCl₂). Veratridine or K⁺ was added to the media 1 hr later and incubated for another hour. In L-type channel experiments, veratridine was added 1 hr after treatment of the cultures with dihydropyridine-type agents. The RNA was extracted from the cultures and processed for RT-PCR assay in triplicates. The signals of NT-3 mRNA were normalized to EF-1α from the same culture. The relative levels of NT-3 mRNA then were measured by normalizing data from the experimental conditions to respective control values. Each experimental condition was repeated two to four times, and all data are presented as mean ± SD.

^*Significantly different from control (p < 0.01, two-tailed Student’s ttest).