Synchronized calcium spiking resulting from spontaneous calcium action potentials in monolayers of NRK fibroblasts.
The correlation between the intracellular Ca2+ concentration ([Ca2+]i) and membrane potential in monolayers of density-arrested normal rat kidney (NRK) fibroblasts was investigated. Using the fluorescent probe Fura-2, spontaneous repetitive spike-like increases in [Ca2+]i (Ca2+ spikes) were observed that were synchronised throughout the entire monolayer. Ca2+ spikes disappeared in Ca(2+)-free solutions and could be blocked by the L-type Ca2+ channel antagonist felodipine. Simultaneous measurements of [Ca2+]i and membrane potential showed that these Ca2+ spikes were paralleled by depolarisations of the plasma membrane. Using patch clamp measurements, action potential-like depolarisations consisting of a fast spike depolarisation followed by a plateau phase were seen with similar kinetics as the Ca2+ spikes. The action potentials could be blocked by L-type Ca2+ channel blockers and were dependent on extracellular Ca2+. The plateau phase was predominantly determined by a Cl- conductance and was dependent on intracellular Ca2+. The presence of voltage-dependent L-type Ca2+ channels in NRK cells was confirmed by patch clamp measurements in single cells. It is concluded that monolayers of density-arrested NRK fibroblasts exhibit spontaneous Ca2+ action potentials leading to synchronised Ca2+ spiking. This excitability of monolayers of fibroblasts may represent a novel Ca2+ signaling pathway in electrically coupled fibroblasts, cells that were hitherto considered to be inexcitable.
de Roos
A D
AD
Department of Cell Biology, University of Nijmegen, The Netherlands.
Willems
P H
PH
Peters
P H
PH
van Zoelen
E J
EJ
Theuvenet
A P
AP
D000200:Action Potentials; D000818:Animals; D001920:Bradykinin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002452:Cell Count; D015736:Felodipine / Q000494:pharmacology; D005347:Fibroblasts / Q000378:metabolism; D016257:Fura-2; D007668:Kidney / Q000166:cytology / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008856:Microscopy, Fluorescence; D000442:Octanols / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D000442:Octanols; D015736:Felodipine; D001920:Bradykinin; D002118:Calcium; D016257:Fura-2