Studies of the effect of ionomycin on the KCNQ4 channel expressed in Xenopus oocytes.
The effect of ionomycin on the human KCNQ4 channels expressed in Xenopus leavis oocytes was investigated. KCNQ4 channels expressed in Xenopus oocytes were measured using two-electrode voltage clamp. The activation of KCNQ4 current had slow activation kinetics and low threshold (approximately -50 mV). The expressed current of KCNQ4 showed the half-maximal activation (V(1/2)) was -17.8 mV and blocked almost completely by KCNQ4 channel blockers, linopirdine (300 microM) or bepridil (200 microM). The significant increase of KCNQ4 outward current induced by ionomycin (calcium salt) is about 1.7-fold of control current amplitude at +60 mV and shifted V(1/2) by approximately -8 mV (from -17.8 to -26.0 mV). This effect of ionomycin could be reversed by the further addition of BAPTA-AM (0.3 mM), a membrane-permeable calcium chelator. Furthermore, the increased effect of ionomycin on KCNQ4 current is abolished by pretreatment of linopirdine or bepridil. In contrast, direct cytoplasmic injection of calcium medium (up to 1 mM calcium, 50 nl) did not mimic the effect of ionomycin. In conclusion, the effect of ionomycin on enhancement of KCNQ4 current is independent of intracellular calcium mobilization and possibly acts on intramembrane hydrophobic site of KCNQ4 protein expressed in Xenopus oocytes.
Su
Ching-Chyuan
CC
Department of Biomedical Sciences, Chung Shan Medical University, Taichung, Taiwan, ROC.
Li
Shuan-Yow
SY
Yang
Jiann-Jou
JJ
Su
Mao-Chang
MC
Lin
Min-Jon
MJ
D000818:Animals; D015764:Bepridil / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D004594:Electrophysiology; D007211:Indoles / Q000494:pharmacology; D015640:Ion Channel Gating / Q000187:drug effects*; D015759:Ionomycin / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D051656:KCNQ Potassium Channels / Q000187:drug effects* / Q000502:physiology; D009865:Oocytes / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D014982:Xenopus laevis
D007211:Indoles; D007476:Ionophores; D051656:KCNQ Potassium Channels; C117367:KCNQ4 protein, human; D011725:Pyridines; D015759:Ionomycin; D015764:Bepridil; C061017:linopirdine; D002118:Calcium