A toxin fraction (FTX) from the funnel-web spider poison inhibits dihydropyridine-insensitive Ca2+ channels coupled to catecholamine release in bovine adrenal chromaffin cells.
In adrenal chromaffin cells, depolarization-evoked Ca2+ influx and catecholamine release are partially blocked by blockers of L-type voltage-sensitive Ca2+ channels. We have now evaluated the sensitivity of the dihydropyridine-resistant components of Ca2+ influx and catecholamine release to a toxin fraction (FTX) from the funnel-web spider poison, which is known to block P-type channels in mammalian neurons. FTX (1:4,000 dilution, with respect to the original fraction) inhibited K(+)-depolarization-induced Ca2+ influx by 50%, as monitored with fura-2, whereas nitrendipine (0.1-1 microM) and FTX (3:3), a synthetic FTX analogue (1 mM), blocked the [Ca2+]i transients by 35 and 30%, respectively. When tested together, FTX and nitrendipine reduced the [Ca2+]i transients by 70%. FTX or nitrendipine reduced adrenaline and noradrenaline release by approximately 80 and 70%, respectively, but both substances together abolished the K(+)-evoked catecholamine release, as measured by HPLC. The omega-conotoxin GVIA (0.5 microM) was without effect on K(+)-stimulated 45Ca2+ uptake. Our results indicate that FTX blocks dihydropyridine- and omega-conotoxin-insensitive Ca2+ channels that, together with L-type voltage-sensitive Ca2+ channels, are coupled to catecholamine release.
Duarte
C B
CB
Center for Cell Biology, University of Coimbra, Portugal.
Rosario
L M
LM
Sena
C M
CM
Carvalho
A P
AP
D000311:Adrenal Glands / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D002478:Cells, Cultured; D002838:Chromaffin System / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D004594:Electrophysiology; D009568:Nitrendipine / Q000494:pharmacology*; D010456:Peptides, Cyclic / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology*; D020866:omega-Conotoxin GVIA
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D002395:Catecholamines; D010456:Peptides, Cyclic; D013111:Spider Venoms; D020866:omega-Conotoxin GVIA; D009568:Nitrendipine; D011188:Potassium; D002118:Calcium