Effect of tetrandrine on free intracellular calcium in cultured calf basilar artery smooth muscle cells.
Abstract
AIM: To study the effects of tetrandrine (Tet) on extracellular Ca2+ influx and
intracellular Ca2+ release in cultured calf basilar artery smooth muscle cells.
METHODS: Free intracellular calcium was examined by a system of measurement of
AR-CM-MIC, using Fura 2-AM as a fluorescent indicator.
RESULTS: In the presence of extracellular Ca2+ 1.3 mmol/L, no significant effect
of Tet on resting [Ca2+]i was found. KCl 20, 40, and 60 mmol/L triggered a
sustained rise in [Ca2+]i, pretreatment with Tet inhibited the elevation of
[Ca2+]i induced by KCl in concentration-dependent manner, Tet at high
concentration (100 micromol/L) almost abolished the rise of [Ca2+]i evoked by
KCl. Caffeine 10 mmol/L only produced a transient increase of [Ca2+]i, which
spontaneously declined back to resting levels. Tet 10-30 micromol/L had no effect
on caffeine-induced [Ca2+]i transient peak. Tet at high concentration (100
micromol/L), however, reduced the [Ca2+]i transient peak induced by caffeine.
Phenylephrine (PE) 10 mmol/L produced a rapid transient peak and a distinct
sustained elevation in [Ca2+]i in the presence of extracellular Ca2+. In the
absence of extracellular Ca2+ containing egtazic acid (EGTA), PE only produced a
rapid transient peak in [Ca2+]i. Pretreatment of Tet (10-100 micromol/L)
inhibited the sustained elevation in [Ca2+]i induced by PE in a
concentration-dependent manner. However, only 100 micromol/L of Tet inhibited the
transient peak in [Ca2+]i induced by PE both in the presence of extracellular
Ca2+ 1.3 mmol/L and in the absence of extracellular Ca2+ containing EGTA.
CONCLUSION: Tet inhibited the Ca2+ influx from the extracellular site via
voltage-activated Ca2+ channel and PE-receptor-operated Ca2+ channel. At a high
concentration, Tet may inhibit the Ca2+ release from sarcoplasmic reticulum (SR)
or refilling of intracellular calcium store in cerebral artery smooth muscle
cells.
Keywords:
intracellular Ca2+ release in cultured calf basilar artery smooth muscle cells.
METHODS: Free intracellular calcium was examined by a system of measurement of
AR-CM-MIC, using Fura 2-AM as a fluorescent indicator.
RESULTS: In the presence of extracellular Ca2+ 1.3 mmol/L, no significant effect
of Tet on resting [Ca2+]i was found. KCl 20, 40, and 60 mmol/L triggered a
sustained rise in [Ca2+]i, pretreatment with Tet inhibited the elevation of
[Ca2+]i induced by KCl in concentration-dependent manner, Tet at high
concentration (100 micromol/L) almost abolished the rise of [Ca2+]i evoked by
KCl. Caffeine 10 mmol/L only produced a transient increase of [Ca2+]i, which
spontaneously declined back to resting levels. Tet 10-30 micromol/L had no effect
on caffeine-induced [Ca2+]i transient peak. Tet at high concentration (100
micromol/L), however, reduced the [Ca2+]i transient peak induced by caffeine.
Phenylephrine (PE) 10 mmol/L produced a rapid transient peak and a distinct
sustained elevation in [Ca2+]i in the presence of extracellular Ca2+. In the
absence of extracellular Ca2+ containing egtazic acid (EGTA), PE only produced a
rapid transient peak in [Ca2+]i. Pretreatment of Tet (10-100 micromol/L)
inhibited the sustained elevation in [Ca2+]i induced by PE in a
concentration-dependent manner. However, only 100 micromol/L of Tet inhibited the
transient peak in [Ca2+]i induced by PE both in the presence of extracellular
Ca2+ 1.3 mmol/L and in the absence of extracellular Ca2+ containing EGTA.
CONCLUSION: Tet inhibited the Ca2+ influx from the extracellular site via
voltage-activated Ca2+ channel and PE-receptor-operated Ca2+ channel. At a high
concentration, Tet may inhibit the Ca2+ release from sarcoplasmic reticulum (SR)
or refilling of intracellular calcium store in cerebral artery smooth muscle
cells.