AMPLIFICATION OF EPSPS BY LOW NI2-SENSITIVE AND AMILORIDE-SENSITIVE CA2+ CHANNELS IN APICAL DENDRITES OF RAT CA1 PYRAMIDAL NEURONS()

Distal synaptic input to hippocampal CA1 pyramidal neurons was evoked by electrical stimulation of afferent fibers in outer stratum radiatum . Whole cell recordings from CA1 cell somata served to monitor excitat ory postsynaptic potential (EPSP) envelopes after dendritic processing . To probe a functional role of low-voltage-activated Ca2+ current [or T current (I-T)] in the apical dendrite, EPSP recordings were combine d with local application of antagonists of I-T. Dendritic application of low concentrations of Ni2+ (5 mu M) and amiloride (50 mu M) reduced EPSP amplitude measured at the soma (resting membrane potential -70 m V) by 33.0 +/- 2.9% (mean +/- SE, n = 27) and 27.0 +/- 2.1% (n = 26), respectively. No appreciable effect on EPSP time course was observed. As expected from the voltage dependence of IT activation, the inhibito ry effect of both antagonists was strongly attenuated when EPSPs were recorded at hyperpolarized membrane potential (-90 mV). In contrast to dendritic application, somatic application of Ni2+ or amiloride produ ced only weak reduction of EPSP amplitude. Our data indicate that dend ritic low Ni2+- and amiloride-sensitive Ca2+ channels giving rise pred ominantly to I-T can produce substantial amplification of synaptic inp ut. We thus propose that these channels represent an important compone nt of subthreshold signal integration in apical dendrites of CA1 pyram idal cells.