Figure 3.

Palytoxin (PTX) transforms Na⁺,K⁺-ATPase pumps into channels, one Na⁺,K⁺-ATPase pump at a time. (a,b) Macroscopic currents induced by the application of 100 nM PTX to outside-out patches excised from guinea-pig ventricular myocytes, bathed in approximately 160 mM Na⁺ solutions, and held at −40 mV, (a) with 5 mM MgATP or (b) with no ATP present in the internal solution; note very different current scales in (a) versus (b). (c,d) Representative palytoxin-induced single-channel recordings from outside-out myocyte patches, held at −70 mV and bathed in approximately 160 mM Na⁺ solutions; dashed lines marked C and O indicate closed and open current levels, respectively. (c) A patch with 5 mM MgATP in the pipette was exposed to 50 pM PTX, which was quickly removed (at second arrow) once the channel opened; long open bursts characterized the gating behaviour of the channel, which remained active for approximately 2 hours. (d) Trace from a patch without pipette ATP, showing gating behaviour shortly after the removal of unbound PTX: open bursts were of shorter duration than seen in the presence of MgATP, and longer closed periods were more frequent. (Adapted from Artigas & Gadsby 2002.)