Ion channels in opossum kidney cells.

This review discusses the activation of ion transport pathways during regulatory volume decrease in opossum kidney (OK) cells. OK cells regulate their volume when exposed to a hypotonic medium. The changes in cell volume are caused by activation of ion transport pathways and the accompanying osmotically driven water movement so that the increased cell volume returns toward physiological levels. The reshrinking of hypotonically swollen cells is termed regulatory volume decrease. In OK cells separate K+ and Cl- conductances are activated. The Na+/H+ cotransport system seems not to be involved. The potassium pathway is mediated by a K+ channel with a slope conductance of about 12 pS. The occasionally observed widely distributed Ca2(+)- and voltage-dependent K+ channel of large unit conductance (120 pS) seems not to be involved. The volume regulatory decrease is accompanied by a cell depolarization from a resting potential of about -60 mV to about -20 mV followed by a repolarization. It will be discussed whether the depolarization is caused by the observed activation of stretch-sensitive ion channels of about 30 and 40 pS, respectively. The transient behavior of the cell volume parallels the time-dependent change of the total membrane current. For both recording techniques the volume regulatory decrease can be blocked by quinine. In addition an inward rectifying K+ channel of about 80 pS has been observed in high KCl solution.