Dihydropyridine-sensitive L-type Ca2+ channels in human foreskin fibroblast cells. Characterization of activation with the growth factor Lys-bradykinin.
We have previously characterized the calcium response of cultured human fibroblasts (HSWP cells) to stimulation by the mitogen Lys-bradykinin (BK). We have reported a biphasic response which includes a rapid rise to a peak that appears to result from mobilization of internal calcium, and a plateau phase, which is due to influx of external calcium (Byron, K., Babnigg, G., Villereal, M. L. (1992) J. Biol. Chem. 267, 108-118). In this paper we examine participation of L-type voltage operated calcium channels in the calcium entry phase of BK-stimulated HSWP cells. We show that there is an increase in 45Ca2+ uptake and an increase in intracellular free calcium concentration ([Ca2+]i) as measured by fura-2, when HSWP cells are stimulated with the L-channel agonist Bay K 8644 under depolarizing conditions. Furthermore, both of these effects are inhibited by low doses of the dihydropyridine antagonist nitrendipine. We also report that BK stimulation of 45Ca2+ uptake can be significantly inhibited by low doses of nitrendipine, while nitrendipine treatment has no effect on the BK-induced rise in [Ca2+]i, as measured by fura-2. These results suggest that under normal conditions the portion of the BK-stimulated Ca2+ influx which is mediated by a nitrendipine-sensitive entry pathway is invisible to the fura-2 technique used to measure [Ca2+]i. This suggest that the nitrendipine-sensitive influx pathway admits calcium preferentially into an intracellular store that is isolated from fura-2. This idea is supported by the observation that in media where calcium has been replaced by 2 mM Ba2+ nitrendipine inhibits most of the BK-stimulated Ba2+ influx.
Baumgarten
L B
LB
Department of Pharmacological and Physiological Sciences, University of Chicago, Illinois 60637.
Toscas
K
K
Villereal
M L
ML
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D016257:Fura-2; D006801:Humans; D015640:Ion Channel Gating; D007609:Kallidin / Q000494:pharmacology*; D009568:Nitrendipine / Q000494:pharmacology
D015220:Calcium Channels; D004095:Dihydropyridines; D007609:Kallidin; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D009568:Nitrendipine; D016257:Fura-2