Ionic basis for excitability of normal rat kidney (NRK) fibroblasts

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Abstract
Ionic membrane conductances of normal rat kidney (NRK) fibroblasts were characterized by whole‐cell voltage‐clamp experiments on single cells and small cell clusters and their role in action potential firing in these cells and in monolayers was studied in current‐clamp experiments. Activation of an L‐type calcium conductance (GCaL) is responsible for the initiation of an action potential, a calcium‐activated chloride conductance (GCl(Ca)) determines the plateau phase of the action potential, and an inwardly rectifying potassium conductance (GKir) is important for the generation of a resting potential of approximately −70 mV and contributes to action potential depolarization and repolarization. The unique property of the excitability mechanism is that it not only includes voltage‐activated conductances (GCaL, GKir) but that the intracellular calcium dynamics is also an essential part of it (via GCl(Ca)). Excitability was found to be an intrinsic property of a fraction (∼25%) of the individual cells, and not necessarily dependent on gap junctional coupling of the cells in a monolayer. Electrical coupling of a patched cell to neighbor cells in a small cluster improved the excitability because all small clusters were excitable. Furthermore, cells coupled in a confluent monolayer produced broader action potentials. Thus, electrical coupling in NRK cells does not merely serve passive conduction of stereotyped action potentials, but also seems to play a role in shaping the action potential. J. Cell. Physiol. 196: 493–503, 2003.