A patch-clamp study of the Ca2+ mobilization from internal stores in bovine aortic endothelial cells. I. Effects of caffeine on intracellular Ca2+ stores.
The effects of agents known to interfere with Ca2+ release processes of endoplasmic reticulum were investigated in bradykinin (BK)-stimulated bovine aortic endothelial cells (BAE cells), via the activation of Ca(2+)-activated potassium channels [K(Ca2+) channels]. In cell-attached patch experiments, the external application of caffeine (1 mM) caused a brief activation of K(Ca2+) channels in Ca(2+)-free and Ca(2+)-containing external solutions. The application of BK (10 nM) during cell stimulation by caffeine (1-20 mM) invariably led to a drastic channel activation which was maintained during a recording period longer than that observed in caffeine-free conditions. In addition, the cell exposure to caffeine (20 mM) during the BK stimulation enhanced systematically the channel activation process. Since a rapid inhibition of BK-evoked channel activity was also produced by removing caffeine from the bath medium, it is proposed that the sustained single-channel response recorded in the concomitant presence of both agents was due to their synergic action on internal stores and/or the external Ca2+ entry pathway resulting in an increased [Ca2+]i. In addition, the local anesthetic, procaine, depressed the initial BK-induced K(Ca2+) channel activity and completely blocked the secondary phase of the channel activation process related to the external Ca2+ influx into stimulated cells. In contrast, this blocking effect of procaine was not observed on the initial caffeine-elicited channel activity and could not suppress the external Ca(2+)-dependent phase of this channel activation process. Our results confirm the existence of at least two pharmacologically distinct types of Ca(2+)-release from internal stores in BAE cells: an inositol 1,4,5-triphosphate (InsP3)-dependent and a caffeine-induced Ca(2+)-release process.
Thuringer
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Département de Physiologie, Université de Montréal, Québec, Canada.
Sauvé
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D000818:Animals; D001011:Aorta / Q000166:cytology*; D001692:Biological Transport / Q000502:physiology; D001920:Bradykinin / Q000494:pharmacology; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000032:analysis / Q000378:metabolism* / Q000493:pharmacokinetics; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004730:Endothelium, Vascular / Q000737:chemistry / Q000166:cytology* / Q000378:metabolism*; D015221:Potassium Channels / Q000502:physiology; D011343:Procaine / Q000494:pharmacology
D015221:Potassium Channels; D002110:Caffeine; D011343:Procaine; D001920:Bradykinin; D002118:Calcium