[Catecholamine secretion from adrenal chromaffin cells].
The effect of palytoxin (PTX) on catecholamine (CA) secretion from cultured bovine adrenal chromaffin cells was examined. PTX (greater than 10(-10) M) induced CA secretion concentration-dependently. About 40-50% of the total cellular CA was secreted during a 20 min incubation with 3 x 10(-8) M PTX. PTX caused increases in [22Na](+)- and [45Ca](2+)-influxes into the cells, which were not affected by TTX. PTX-induced CA secretion and [22Na](+)- and [45Ca](2+)-influxes were significantly inhibited by quinidine and aprindine, antiarrhythmic drugs. Ca(2+)-channel blockers such as nifedipine, verapamil, Co2+, and Cd2+ inhibited both CA secretion and [45Ca](2+)-influx induced by PTX. These results indicated that PTX-induced CA secretion was mediated by activation of Na(+)-dependent, TTX-insensitive voltage-dependent Ca(2+)-channels. PTX-induced [22Na](+)-influx was inhibited by amiloride, an inhibitor of the Na(+)-H+ exchange system, suggesting that the Na(+)-H+ exchange mechanism might be involved in PTX-induced [22Na](+)-influx into the cells. The effects of flavonoids on CA secretion from permeabilized adrenal chromaffin cells were examined. CA secretion from the cells in response to a direct Ca2+ challenge was inhibited by quercetin (greater than 10(-5) M) and apigenin (greater than 10(-5) M). These flavonoids also inhibited phorbol ester TPA-induced CA secretion. Therefore, the inhibitory effects of flavonoids on CA secretion were thought to be attributed to their inhibitory effects on PKC.
Department of Pharmacology, Tokushima University School of Medicine, Japan.
M
M
Oka
K
K
Morita
M
M
Yoshizumi
H
H
Houchi
Y
Y
Ishimura
Y
Y
Masuda
D000178:Acrylamides; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D003064:Cnidarian Venoms / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D000095702:Polyether Toxins
D000178:Acrylamides; D002395:Catecholamines; D003064:Cnidarian Venoms; D005419:Flavonoids; C010272:palytoxin; D000095702:Polyether Toxins