Activation of two types of Ca2+-permeable nonselective cation channel by endothelin-1 in A7r5 cells.
1. In A7r5 cells loaded with the Ca2+ indicator fura-2, we examined the effect of a Ca2+ channel blocker SK&F 96365 on increases in intracellular free Ca2+ concentrations ([Ca2+]i) and Mn2+ quenching of fura-2 fluorescence by endothelin-1 (ET-1). Whole-cell patch-clamp was also performed. 2. Higher concentrations (> or = 10 nM) of ET-1 (higher [ET-1]) evoked a transient peak and a subsequent sustained elevation in [Ca2+]i: removal of extracellular Ca2+ abolished only the latter. A blocker of L-type voltage-operated Ca2+ channel (VOC) nifedipine at 1 microM reduced the sustained phase to about 50%, which was partially sensitive to SK&F 96365 (30 microM). 3. Lower [ET-1] (< or = 1 nM) evoked only a sustained elevation in [Ca2+]i which depends on extracellular Ca2+. The elevation was partly sensitive to nifedipine but not SK&F 96365. 4. In the presence of 1 microM nifedipine, higher [ET-1] increased the rate of Mn2+ quenching but lower [ET-1] had little effect. 5. In whole-cell recordings, both lower and higher [ET-1] induced inward currents at a holding potential of -60 mV with linear I-V relationships and reversal potentials close to 0 mV. The current at lower [ET-1] was resistant to SK&F 96365 but was abolished by replacement of Ca2+ in the bath solution with Mn2+. The current at higher [ET-1] was abolished by the replacement plus SK&F 96365. 6. In a bath solution containing only Ca2+ as a movable cation, ET-1 evoked currents: the current at lower [ET-1] was sensitive to Mn2+, whereas that at higher [ET-1] was partly sensitive to SK&F 96365. 7. These results indicate that in addition to VOC, ET-1 activates two types of Ca2+-permeable nonselective cation channel depending on its concentrations which differ in terms of sensitivity to SK&F 96365 and permeability to Mn2+.
Department of Neurosurgery, Kyoto University Faculty of Medicine, Japan.
Y
Y
Iwamuro
S
S
Miwa
T
T
Minowa
T
T
Enoki
X F
XF
Zhang
M
M
Ishikawa
N
N
Hashimoto
T
T
Masaki
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002460:Cell Line; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects*; D007093:Imidazoles / Q000494:pharmacology; D007473:Ion Channels / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D051381:Rats
D002121:Calcium Channel Blockers; D007093:Imidazoles; D007473:Ion Channels; C063159:1-(2-(3-(4-methoxyphenyl)propoxy)-4-methoxyphenylethyl)-1H-imidazole; D009543:Nifedipine; D002118:Calcium