L-TYPE CALCIUM CHANNELS MAY REGULATE NEURITE INITIATION IN CULTURED CHICK-EMBRYO BRAIN NEURONS AND N1E-115 NEUROBLASTOMA-CELLS

The intracellular free Ca2+ concentration, [Ca2+]i, plays an important role in regulating neurite growth in cultured neurons. Insofar as [Ca2+]i is partly a function of Ca2+ influx through voltage-sensitive calcium channels (VSCC), Ca2+ entry through VSCC should influence neurite growth. Vertebrate neurons may possess several types of VSCC. The most frequently described VSCC types are usually designated L, T and N. In most preparations, these VSCC types respond differently to certain pharmacological agents, including Cd2+, Ni2+, the dihydropyridines nifedipine and BAY K8644, and the aminoglycoside antibiotics. We used these agents to study the role of Ca2+ influx in regulating neurite initiation and length in cultures of chick embryo brain neurons and N1E-115 mouse neuroblastoma cells. In chick neurons, nifedipine and Cd2+ (<50 μM), which have been reported to inhibit L-type channels, reduced neurite initiation but not mean neurite length. Ni2+ (<100 μM), reported to inhibit T-type channels, had no effect on either initiation or length. Low concentrations of most aminoglycosides (<300 μM), reported to inhibit N-type channels, had no effect on neurite initiation, but high concentrations of streptomycin (>300 μM), reported to inhibit both L- and N-type channels, reduced neurite initiation. BAY K8644, which enhances current flow through L-type channels, had no effect except at high concentration (50 μM), which inhibited initiation. N1E-115 neuroblastoma cells have been reported to contain L-type and T-type channels, but thus far no channel similar to the N-type has been described. In cultured N1E-115 cells, nifedipine (5 μM), Cd2+ (5 μM), and streptomycin (200 μM) reduced neurite initiation, while nickel (50 μM) and neomycin (100 μM) did not affect initiation. None of these agents altered neurite length. In N1E-115 cells, whole-cell voltage clamp recordings showed that nifedipine and Cd2+ inhibited L-type channels but not T-type channels, while Ni2+ inhibited T-type channels but not L-type channels. Streptomycin slightly inhibited L-type channels but enhanced current flow through T-type channels. Neomycin slightly inhibited both channel types. These data indicate that neurite initiation in these two cell types may be modulated by Ca2+ influx through L-type channels, but not T- or N-type channels. Neurite length was not significantly influenced by any of the agents tested, suggesting that Ca2+ influx through VSCC may not affect neurite elongation. © 1990.