Four types of potassium currents in motor nerve terminals of snake

Abstract

The experiments were perfomed on transversus abdominis muscle ofElaphe dione by subendothelial recording. The results indicate that in snake motor nerve endings there exist four types of K⁺ channels, i.e. voltagedependent fast and slow K⁺ channels, Ca²⁺-activated K⁺ channel and ATP-sensitive K⁺ channel. (i) The typical wave form of snake terminal current was the double-peaked negativity in standard solution. The first peak was attributed to Na⁺ inflm (I_Na) in nodes of Ranvier. The second one was blocked by 3,4-aminopyridine (3,4-DAP) or tetraethylammonium (TEA), which corresponded to fast K⁺ outward current (I^k.f) through the fast K⁺ channels in terminal part. (ii) After I_K.F as well as the slow K⁺ current (I_K.S) were blocked by 3, 4-DAP, the TEA-sensitive Ca^{2 +}-dependent K⁺ current (I_K(Ca)) passing through Ca^{2 +}-activated K⁺ channel was revealed, whose amplitude depended on [K⁺]_o and [ca²⁺ ]_o. It was blocked by Ba²⁺, Cd²⁺ or Co²⁺. (iii) I_K.F and I_K(Ca) were blocked by TEA, while I_{K. S} was retained. It was sensitive to 3,4-DAP, partially blocked by ethanol (200 mmol/L) or β-bungarotoxin (2 μmol/L), and enhanced by low pH (6.4–6.7). This is the first report that certain current component of motor nerve terminal is sensitive to pH in the range of 6. 4–7. 5. (iv) That diazoxide (200 μmol/L) increased the second negative peak and the effect was eliminated after further addition of glibenclamide (50 μmol/L) was taken as evidence for the presence of ATP-sensitive K⁺ current (I_k.atp) at snake nerve terminal.