Overview
- Shahidi, S. et al. (1993) Biochem. Biophys. Acta 1157, 74.
Alomone Labs Apamin inhibits KCa2.1 (SK1) channel heterologously expressed in Xenopus oocytes.Voltage clamped whole oocytes current expressing KCa2.1 was recorded continuously in low Cl- concentration at 5 mV holding potential. At the indicated time, Ca2+ was injected and an outward current developed. One minute later 1 µM Apamin (#STA-200) was perfused to the bath, resulting in about 66% inhibition in the amplitude of this Ca2+-dependent current, which completely recovered upon toxin wash.
Alomone Labs Apamin inhibits SK2 channels in transfected HEK-293 cells.A. Time course of Apamin (#STA-200) action on SK2 channels. Current amplitudes were plotted as a function of time. Membrane potential was held at -80 mV and cells were stimulated by a 150 ms voltage ramp from -120 mV to +60 mV every 10 sec. 1 nM Apamin was perfused during 2.5 min as indicated by the bar at -10 mV. B. Superimposed examples of SK2 channel current in the absence (control, black) and presence of 1 nM Apamin (green) (taken from the experiment in A).
Apamin is a natural peptide isolated and purified from Apis mellifera bee venom. Apamin blocks small conductance Ca2+-activated K+ channels (SK). It is specific for the SK1-3 isoforms, but ineffective in blocking other calcium activated K+ channels2. In mammalian cell lines, Apamin blocks expressed hSK1 with an IC50 of ~10 nM3, rSK1 and rSK2 with IC50 of ~3 and <1 nM respectively4 and liver rSK3 with IC50 <1 nM.5 In Jurkat T-cells, 5 nM of Apamin blocks 70% of hSK2 currents.6
Blocking these channels with Apamin slows down neuronal activity after hyperpolarization7, as well as smooth muscle contraction8 and catecholamine secretion in adrenal glands.9 Electrophysiology application of long (~400 ms) voltage ramps, covering the whole physiological range (-160 to +40 mV), in the whole cell patch-clamp or voltage clamp configurations, before and after bath perfusion of the drug, allows the detection of the blocked channel currents (by comparison).1
