title: Inhibition of high K+ and norepinephrine-induced free intracellular calcium by tetrandrine in dissociated rabbit retina cells.
abstract: The effect of tetrandrine (Tet) on the changes of intracellular free Ca2+ concentration ([Ca2+]i) induced by high concentration of K+ and norepinephrine is dissociated rabbit retina cells were studied. The changes of [Ca2+]i were reflected by the fluorescent indicator, Fura-2/AM, employed. The resting [Ca2+]i was 223 +/- 27 nM in Hank's solution containing 1.3 mM Ca2+. Tet at 30 microM did not affect the resting [Ca2+]i when the extracellular Ca2+ concentration was in the range of 0-2 mM. Tet at 1-100 microM suppressed the [Ca2+]i elevation induced by high concentration of K+ in a concentration-dependent manner. When the concentration of K+ was 50 mM IC50 for Tet was 10.9 microM. Although Tet at high concentration (30 microM) suppressed the [Ca2+]i increases induced by norepinephrine (0.1-100 nM) in the presence of Ca2+ at 1.3 mM, failed to do the same at lower concentration of Tet (1-10 microM), however, Tet at 30 microM did not effect the release of intracellular Ca2+ stored in the sarcoplasmic reticulum in the Ca(2+)-free Hank's solution. These results indicate that Tet is able to block Ca2+ influx from extracellular site via voltage-sensitive ionic channels and at high concentration via receptor-operated ionic channels in retina cells.
authors.affiliation: Department of Pharmacology, Nanjing Medical University, China.
authors.forename: B
authors.initials: B
authors.lastname: Xuan
authors.forename: M Y
authors.initials: MY
authors.lastname: Zhang
authors.forename: F
authors.initials: F
authors.lastname: Liu
authors.forename: J G
authors.initials: JG
authors.lastname: Xiao
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000470:Alkaloids / Q000494:pharmacology*; D000818:Animals; D044182:Benzylisoquinolines; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002478:Cells, Cultured / Q000187:drug effects; D066298:In Vitro Techniques; D009638:Norepinephrine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D011817:Rabbits; D012160:Retina / Q000187:drug effects* / Q000378:metabolism; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D000316:Adrenergic alpha-Agonists; D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; C009438:tetrandrine; D011188:Potassium; D002118:Calcium; D009638:Norepinephrine