Prostaglandin E2 activates Ca2+ channels in bovine adrenal chromaffin cells.
We have demonstrated that prostaglandin E2 (PGE2) treatment of bovine adrenal chromaffin cells results in a sustained elevation of intracellular Ca2+ concentration ([Ca2+]i) in these cells. Because the continued elevation of [Ca2+]i was dependent on extracellular Ca2+ concentration, it can be assumed that the PGE2-induced [Ca2+]i increase is due, at least in part, to an opening of membrane Ca2+ channels. In this study, we used electrophysiological methods to examine the mechanism of the PGE2-induced [Ca2+]i increase directly. Puff application of PGE2 to the external medium resulted in a prolonged depolarization in about half of the chromaffin cells examined. In whole-cell voltage-clamp recordings, an increase in inward current was observed over a 6-7 min period following bath application of PGE2 (greater than or equal to 10 microM), even in the absence of external Na+. This inward current was abolished when the recordings were made with the cells in a Ca2(+)-free medium, but it was not inhibited by Mn2+, a blocker of voltage-dependent Ca2+ channels. In cell-attached patch-clamp configuration, PGE2 produced an increase in the opening frequency of inward currents. The reversal potential of the PGE2-induced currents was about +40 mV, which is close to the reversal potential of the Ca2+ channel. The opening frequency was not affected by membrane potential changes. In inside-out patch-clamp configuration, inositol 1,4,5-trisphosphate (2 microM) added to the cytoplasmic side activated the Ca2(+)-channel currents, but PGE2 was ineffective when applied to the cytoplasmic side. These results suggest that PGE2 activates voltage-independent Ca2+ channels in chromaffin cells through a diffusible second messenger, possibly inositol 1,4,5-trisphosphate.
Mochizuki-Oda
N
N
Department of Cell Biology, Osaka Bioscience Institute, Suita, Japan.
Mori
K
K
Negishi
M
M
Ito
S
S
D000313:Adrenal Medulla / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D002417:Cattle; D002838:Chromaffin System / Q000187:drug effects / Q000502:physiology*; D015232:Dinoprostone / Q000494:pharmacology*; D004553:Electric Conductivity; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D015290:Second Messenger Systems
D015220:Calcium Channels; D015544:Inositol 1,4,5-Trisphosphate; D015232:Dinoprostone; D002118:Calcium