The role of Ca 2+ channels of the L-type in neurotransmitter plasticity of cultured sympathetic neurons

Abstract

We have studied the effects of Ca 2+ antagonists and agonists on the development of choline acetyltransferase (ChAT), tyrosine hydroxylase (TOH) and acetylcholinesterase (AChE) in cultures of rat sympathetic neurons maintained for 6–9 days in low K + (5 mM) or high K + (35 mM) medium. Previous experiments have shown that high K + medium increases TOH activity and TOH-mRNA level up to 3.5-fold and depresses the development of AChE, in particular of its asymmetric A 12 form. Moreover, high K + medium inhibits ChAT induction by 90% in muscle-conditioned medium (Raynaud et al., Dev. Biol., 119 (1987) 305–312; 121 (1987) 548–558). None of the Ca 2+ antagonists tested affected the development of ChAT, TOH or AChE in low K + medium. In high K + medium, nitrendipine (3 μM) or fluspirilene (1 μM) fully restored ChAT induction by conditioned medium to the level observed in low K + medium. Other drugs (1 μM) gave partial reversion: flunarizine > (+)-PN 200-110 > (−)-D-888 > cinnarizine = lidoflazine. On the other hand, ChAT induction was not restored by a calmodulin inhibitor, calmidazolium (1 μM). Fluspirilene, PN 200-110, and nitrendipine also totally abolished TOH induction by high K + medium; fluspirilene (1 μM) suppressed the inhibitory effect of high K + medium on AChE development and restored the development of A 12 AChE. Conditioned medium also depresses AChE and blocks the development of A 12 AChE (Swerts et al., Dev. Biol., 103 (1984) 230–234), but these effects were insensitive to fluspirilene. The Ca 2+ agonist Bay K 8644 (1 μM) potentiated the effects of elevated K + on both ChAT and TOH. The data suggest that the effects of long-term depolarization on ChAT, TOH and AChE are mediated by Ca 2+ entry specifically through voltage-sensitive channels of the L-type. Our results on cultured sympathetic neurons raise the possibility that Ca 2+ antagonists, which are widely used clinically, may affect the expression of neurotransmitter phenotypic traits in vivo and interfere with trans-synaptic induction of enzymes.