High-voltage-activated Ca2+ currents show similar patterns of expression in stellate and pyramidal cells from rat...

High-voltage-activated (HVA) Ca2+ 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 Ba2+ as the charge carrier. In both neuronal types, the amplitude of total HVA Ba2+ currents (IBas) 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 IBa expression reached stable levels, IBa density per unit of membrane area was not different in stellate versus pyramidal cells. The same was also observed when Ca2+, instead of Ba2+, 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 Ca2+ channel subtypes. In both cell types, approximately 52-55% of total IBas was abolished by the L-type channel blocker, nifedipine (10 microM), approximately 23-30% by the N-type channel blocker, omega-conotoxin GVIA (1 microM), approximately 22-24% by the P/Q-type channel blocker, omega-agatoxin IVA (100 nM), and approximately 11-13% remained unblocked (R-type current) after simultaneous application of L-, N-, and P/Q-type channel blockers. The Cav 2.3 (alpha1E) channel blocker, SNX-482 (100 nM), abolished approximately 57-62% of total R-type current. We conclude that HVA Ca2+ currents are expressed according to similar patterns in the somata and proximal dendrites of stellate and pyramidal cells of rat EC layer II.