High-voltage-activated Ca 2+ currents show similar patterns of expression in stellate and pyramidal cells from rat entorhinal cortex layer II

Abstract

High-voltage-activated (HVA) Ca 2+ currents were studied in acutely isolated neurons from rat entorhinal cortex (EC) layer II. Stellate and pyramidal cells, the two main neuronal types of this structure, were visually identified based on morphological criteria. HVA currents were recorded by applying the whole-cell, patch-clamp technique, using 5-mM Ba 2+ as the charge carrier. In both neuronal types, the amplitude of total HVA Ba 2+ currents ( I Bas) showed a significant tendency to increase with postnatal age in the time window considered [postnatal day 15 (P15) to P28–29]. At P20–P29, when I Ba expression reached stable levels, I Ba density per unit of membrane area was not different in stellate versus pyramidal cells. The same was also observed when Ca 2+, instead of Ba 2+, was used as the charge carrier. The pharmacological current subtypes composing total HVA currents were characterized using selective blockers. Again, no significant differences were found between stellate and pyramidal cells with respect to the total–current fractions attributable to specific pharmacological Ca 2+ channel subtypes. In both cell types, ∼52–55% of total I Bas was abolished by the L-type channel blocker, nifedipine (10 μM), ∼23–30% by the N-type channel blocker, ω-conotoxin GVIA (1 μM), ∼22–24% by the P/Q-type channel blocker, ω-agatoxin IVA (100 nM), and ∼11–13% remained unblocked (R-type current) after simultaneous application of L-, N-, and P/Q-type channel blockers. The Ca v 2.3 (α 1E) channel blocker, SNX-482 (100 nM), abolished ∼57–62% of total R-type current. We conclude that HVA Ca 2+ currents are expressed according to similar patterns in the somata and proximal dendrites of stellate and pyramidal cells of rat EC layer II.