The Journal of Neurophysiology Vol. 78 No. 6 December 1997, pp. 3484-3488
Copyright ©1997 The American Physiological Society

Inhibition of Dendritic Calcium Influx by Activation of G-Protein-Coupled Receptors in the Hippocampus

Huanmian Chen and Nevin A. Lambert

Department of Pharmacology and Toxicology, Medical College of Georgia and Veterans Affairs Medical Center, Augusta, Georgia 30912-2300

Chen, Huanmian and Nevin A. Lambert. Inhibition of dendritic calcium influx by activation of G-protein-coupled receptors in the hippocampus. J. Neurophysiol. 78: 3484-3488, 1997. G_i proteins inhibit voltage-gated calcium channels and activate inwardly rectifying K⁺ channels in hippocampal pyramidal neurons. The effect of activation of G-protein-coupled receptors on action potential-evoked calcium influx was examined in pyramidal neuron dendrites with optical and extracellular voltage recording. We tested the hypotheses that 1) activation of these receptors would inhibit calcium channels in dendrites; 2) hyperpolarization resulting from K⁺ channel activation would deinactivate low-threshold, T-type calcium channels on dendrites, increasing calcium influx mediated by these channels; and 3) activation of these receptors would inhibit propagation of action potentials into dendrites, and thus indirectly decrease calcium influx. Activation of adenosine receptors, which couple to G_i proteins, inhibited calcium influx in cell bodies and proximal dendrites without inhibiting action-potential propagation into the proximal dendrites. Inhibition of dendritic calcium influx was not changed in the presence of 50 µM nickel, which preferentially blocks T-type channels, suggesting influx through these channels is not increased by activation of G-proteins. Adenosine inhibited propagation of action potentials into the distal branches of pyramidal neuron dendrites, leading to a three- to fourfold greater inhibition of calcium influx in the distal dendrites than in the soma or proximal dendrites. These results suggest that voltage-gated calcium channels are inhibited in pyramidal neuron dendrites, as they are in cell bodies and terminals and thatG-protein-mediated inhibition of action-potential propagation can contribute substantially to inhibition of dendritic calcium influx.

This article has been cited by other articles:

				M. E. Larkum and J. J. Zhu Signaling of Layer 1 and Whisker-Evoked Ca2+ and Na+ Action Potentials in Distal and Terminal Dendrites of Rat Neocortical Pyramidal Neurons In Vitro and In Vivo J. Neurosci., August 15, 2002; 22(16): 6991 - 7005. [Abstract] [Full Text] [PDF]

				T. Takigawa and C. Alzheimer Phasic and tonic attenuation of EPSPs by inward rectifier K+ channels in rat hippocampal pyramidal cells J. Physiol., February 15, 2002; 539(1): 67 - 75. [Abstract] [Full Text] [PDF]

				B. Mlinar, A. M. Pugliese, and R. Corradetti Selective inhibition of local excitatory synaptic transmission by serotonin through an unconventional receptor in the CA1 region of rat hippocampus J. Physiol., July 1, 2001; 534(1): 141 - 158. [Abstract] [Full Text] [PDF]

				J. J. Zhu and F.-S. Lo Three GABA Receptor-Mediated Postsynaptic Potentials in Interneurons in the Rat Lateral Geniculate Nucleus J. Neurosci., July 15, 1999; 19(14): 5721 - 5730. [Abstract] [Full Text] [PDF]

				V. M. Sandler and W. N. Ross Serotonin Modulates Spike Backpropagation and Associated [Ca2+]i Changes in the Apical Dendrites of Hippocampal CA1 Pyramidal Neurons J Neurophysiol, January 1, 1999; 81(1): 216 - 224. [Abstract] [Full Text] [PDF]