Patch-clamp study of neurones in rat olfactory cortex slices: Properties of a slow post-stimulus afterdepolarizing current (I-ADP)

WHOLE-CELL recordings were made from neurones in slices of rat olfactory cortex (10-19 days old), using potassium methylsulphate-filled pipettes. Positive commands applied from -60 mV in the presence of oxotremorine-M (10-20 mu M, 20 of 30 cells) or trans-ACPD (10-50 mu M, 4 of 9 cells) evoked a slow inward tail current similar to the K+-mediated tail current (I-K,I-ADP) recorded with sharp electrodes. I-ADP was reduced by hyperpolarization; showed a 27% decrease in input conductance at its peak and was depressed by Cd2+, 4AP or high K+ but unaffected by Cs+, Ba2+ or TEA (5 mM). I-ADP was significantly larger in cells between postnatal days 13 and 15 than in younger neurones (10-12 days). These data show that stable whole-cell recordings of I-ADP can be made from olfactory neurones in cortical slices, and support our hypothesis that I-ADP is a slowly reactivating, Ca2+-sensitive K+ conductance.