Multiple components of calcium current in acutely dissociated dentate gyrus granule neurons

Abstract

1. Specific Ca2+ channel blocker were used to isolate and characterize different components of whole cell Ba2+ current in granule neurons acutely dissociated from guinea pig hippocampal slices. 2. Granule cell Ba2+ current peaked around +5 mV, whether elicited by step or ramp commands, and was completely blocked by 100 microM Cd2+. 3. Saturating doses (> or = 5 microM) of the dihydropyridine antagonist, nimodipine, blocked 39% of the total current, and the inhibition was partially reversible. Nimodipine had a greater effect on current at the end of a depolarizing step, suggesting some voltage dependence of its action. 4. Saturating doses (> or = 3 microM) of omega-conotoxin-GVIA irreversibly blocked 21% of the total current and did not occlude subsequent nimodipine inhibition. 5. High concentrations (> or = 100 nM) of omega-agatoxin-IVA irreversibly blocked another 20% of the total current. The effect of omega-Aga-IVA was quite slow, but saturated after several minutes at 200 nM concentration. A high dose (1 microM) produced rapid effects that were used to quantify the magnitude of block. 6. When applied together, all three blockers inhibited nearly the same amount of total current (77%) as would be expected from the sum of each blocker applied individually (80%), suggesting that the three antagonists blocked different channel types. 7. Quantitatively similar results were obtained for the effect of each blocker alone and in combination on currents elicited by depolarizing ramp commands. Ramp currents blocked by each antagonist (difference ramps) all peaked near the same potential as the initial control ramp, indicating very similar activation properties for the three current components. Difference currents elicited by step commands similarly showed little difference among the three components in their kinetics of inactivation during relatively brief (30 ms) depolarizations. With longer steps, however, the omega-CgTX-GVIA-sensitive component showed some inactivation, whereas the omega-Aga-IVA-sensitive current did not inactivate. 8. The component of current resistant to all three blockers (approximately 23% of total current) was not inhibited by omega-conotoxin-MVIIC, but was half blocked by 50 microM Ni2+. This Ni(2+)-sensitive component showed relatively rapid inactivation and peaked at a somewhat lower potential (-10 mV) than the control current. The resistant current was also inactivated by approximately 50% by holding at -60 compared with -80 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

Calcium‐dependent inactivation of high‐threshold calcium currents in human dentate gyrus granule cells

“…Given the scarcity of human dissociated neurones, we did not use specific pharmacological tools to separate the underlying Ca¥ conductances. While in guinea-pig DGGCs at least four different ICa components (T, L, N and P) were demonstrated (Eliot & Johnston, 1994), under our experimental conditions the predominant source of Ca¥ influx into dissociated human granule cells is a HVA ICa composed of up to three Ca¥ conductances. Our recordings also differ from those of Beck et al (1997b) in the substantially smaller peak IBa densities (60 ± 6 pA pF¢ versus the 144·3 ± 24·3 pA pF¢ in their report).…”

Ryanodine produces a low frequency stimulation‐induced NMDA receptor‐independent long‐term potentiation in the rat dentate gyrus in vitro.

“…(Fox, Nowycky & Tsien, 1987;. Ni2+-sensitive low voltage threshold Ca2+ channels have been identified in hippocampal cells, including hippocampal dendrites (Mogul & Fox, 1991;Eliot & Johnston, 1994;. Moreover, subthreshold trains of synaptic potentials have also been…”

Early Emergence of Neural Activity in the Developing Mouse Enteric Nervous System

“…SNX-482 only produced a significant effect on E15.5 duodenum, whereas Ni 2ϩ reduced the transients in E12.5 small intestine as well as E15.5 colon cultures. Because Ni 2ϩ at 50 M blocks R-type as well as T-type Ca 2ϩ channels (Eliot and Johnston, 1994;Bian et al, 2004), we examined the effects of SNX-482 and Ni 2ϩ consecutively on the same cells. In both E12.5 small intestine and E15.5 colon preparations, the change in the [Ca 2ϩ ] i peak in the presence of Ni 2ϩ was significantly greater than in the presence of SNX-482 (p Ͻ 0.05, Student's t test, paired sample for means; n ϭ 125 and n ϭ 115 respectively), suggesting that T-type Ca 2ϩ channels are involved at both ages.…”