Osmosensitivity of an inwardly rectifying chloride current revealed by whole-cell and perforated-patch recordings in cultured rat cortical astrocytes

The osmosensitivity of the inwardly rectifying Cl −current ( IClh), expressed by primary cultured rat neocortical astrocytes long-term treated with dibutyryl cyclic AMP, was investigated in the whole-cell and perforated-patch modes. In whole-cell experiments, whereas hypotonic extracellular solution ( Δ=100 mOsmol) did not cause any change in IClh, hypertonicity produced a slowly developing, ∼40% reversible decrease in current magnitude. By contrast, in perforated-patch experiments, exposure to a less hypertonic saline ( Δ=50 mOsmol) depressed the current to ∼50%, and hypotonicity induced a ∼50% slow increase in IClh. These differences in osmosensitivity between the two experimental modes suggest that the osmoregulation of IClhmay be mediated by complex intracellular mechanism(s), which appear(s) to be partly compromised by the dialysis of the astrocytic cytoplasm.