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 (I(Clh)), 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 (Delta=100 mOsmol) did not cause any change in I(Clh), hypertonicity produced a slowly developing, approximately 40% reversible decrease in current magnitude. By contrast, in perforated-patch experiments, exposure to a less hypertonic saline (Delta=50 mOsmol) depressed the current to approximately 50%, and hypotonicity induced a approximately 50% slow increase in I(Clh). These differences in osmosensitivity between the two experimental modes suggest that the osmoregulation of I(Clh) may be mediated by complex intracellular mechanism(s), which appear(s) to be partly compromised by the dialysis of the astrocytic cytoplasm.