Ionic basis for excitability of normal rat kidney (NRK) fibroblasts.
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 (approximately 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.
Harks
E G A
EG
Department of Cell Biology, University of Nijmegen, Nijmegen, The Netherlands.
Torres
J J
JJ
Cornelisse
L N
LN
Ypey
D L
DL
Theuvenet
A P R
AP
D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D004553:Electric Conductivity; D005347:Fibroblasts / Q000378:metabolism*; D017136:Ion Transport; D007668:Kidney / Q000166:cytology* / Q000378:metabolism; D051381:Rats