Summary
Pre- and postsynaptic fluxes of Ca2+ and K+ were determined concurrently in CA1 of the hippocampus in vitro under conditions where synaptic transmission was blocked. The Ca2+ entry blocker, Ni2+, abolished both pre- and postsynaptic Ca2+-influx and reduced presynaptic K+-efflux by about 20%. Postsynaptic K+-efflux was reduced nearly by 60%. 4-aminopyridine (4-AP) strongly enhanced presynaptic Ca2+-influx but only marginally increased Ca2+-entry into the postsynaptic neurones. At the same time, total K+-efflux from presynaptic sites was increased by about 30% but was unaltered postsynaptically. Finally, tetraethylammonium (TEA) enhanced both pre- and postsynaptic Ca2+-influx. Postsynaptic influx was more profoundly affected than presynaptic. Neither pre- nor postsynaptic efflux of K+ was altered by TEA. The results indicate a complex balance between inward Ca2+ and outward K+ currents in CA1 and that this balance may differ pre- and postsynaptically.
Similar content being viewed by others
References
Aitken PG, Somjen GG (1986) The sources of extracellular potassium accumulation in the CA1 region of hippocampal slices. Brain Res 304: 163–167
Brown DA, Griffith WH (1983) Calcium activated outward current in voltage clamped hippocampal neurones of the guinea pig. J Physiol (Lond) 337: 287–301
Gustaffson B, Galvan M, Grafe P, Wigstrom H (1982) A transient outward current in a mammalian central neurone blocked by 4-aminopyridine. Nature (Lond) 299: 252–254
Haas HL, Wieser HG, Yasargil MG (1983) 4-aminopyridine and fibre potentials in rat and human hippocampal slices. Experentia 39: 114–115
Heinemann U, Jones RSG (1986) Reduction of stimulus evoked postbut not presynaptic calcium influx in rat hippocampus by organic calcium antagonists. Br J Pharmac 87: 5P
Heinemann U, Neuhaus S, Dietzel I (1983) Aspects of K+ regulation in normal and gliotic brain tissue. In: Baldy- Moulinier M, Ingvar DH, Meldrum BS (eds) Cerebral blood flow metabolism and epilepsy. John Libbey and Co Ltd, London Paris, pp 271–278
Herman A, Gorman ALF (1981) Effects of 4-AP on potassium currents in a molluscan neurone. J Gen Physiol 78: 63–86
Hotson JR, Prince DA (1980) A calcium-activated hyperpolarisation follows repetitive firing in hippocampal neurones. J Neurophysiol 43: 409–419
Jones RSG, Heinemann U (1987) Differential effects of calcium entry blockers on pre- and postsynaptic influx of calcium in rat hippocampal slices. Brain Res (in press)
Jones RSG, Kohr G, Heinemann U (1986) Effects of organic and inorganic calcium entry blockers on pre- and postsynaptic calcium entry in rat hippocampal slices. Pflügers Arch 406 (Suppl): R12
Konnerth A, Heinemann U (1983a) Effect of GABA on presumed presynaptic calcium entry in hippocampal slices. Brain Res 270: 185–189
Konnerth A, Heinemann U (1983b) Presynaptic involvement in frequency facilitation in the hippocampal slice. Neurosci Lett 42: 255–260
Lux HD, Neher E (1973) The equilibrium time course of [K+]o in cat cortex. Exp Brain Res 17: 190–205
Marciani MG, Louvel J, Heinemann U (1982) Aspartate induced changes in extracellular free calcium in “in vitro” hippocampal slices of rats. Brain Res 238: 272–277
Rogawski MA, Barker JL (1983) Effects of 4-aminopyridine on calcium action potentials and calcium current under voltage clamp in spinal neurones. Brain Res 280: 180–185
Sah P, Gibb AJ, Gage PW (1987) A delayed rectifier in acutely dissociated adult hippocampal neurones. Neurosci Lett Suppl 27: S119
Schuberth P, Heinemann U, Kolb R (1986) Differential effects of adenosine on pre- and postsynaptic calcium fluxes. Brain Res 376: 382–386
Schwartzkroin PA, Prince DA (1980) Effects of TEA on hippocampal neurones. Brain Res 238: 169–181
Segal M, Barker JL (1984) Rat hippocampal neurones in culture: potassium conductances. J Neurophysiol 51: 1409–1433
Segal M, Barker JL (1986) Rat hippocampal neurones in culture: Ca2+ and Ca2+-dependant K+-conductances. J Neurophysiol 55: 751–766
Thomson SH (1977) Three pharmacologically distinct potassium conductances in molluscan neurones. J Physiol 265: 465–488
Ulbricht, W, Wagner HH (1978) Block of potassium channels of the nodal membranes by 4-aminopyridine and its removal by depolarisation. Pflügers Arch 267: 77–87
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Jones, R.S.G., Heinemann, U. Preand postsynaptic K+ and Ca2+ fluxes in area CA1 of the rat hippocampus in vitro: effects of Ni2+, TEA and 4-AP. Exp Brain Res 68, 205–209 (1987). https://doi.org/10.1007/BF00255246
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00255246