4 TYPES OF POTASSIUM CURRENTS IN MOTOR-NERVE TERMINALS OF SNAKE

The experiments were perfomed on transversus abdominis muscle of Elaph e dione by subendothelial recording. The results indicate that in snak e motor nerve endings there exist four types of K+ channels, i.e. volt age-dependent 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 fi rst peak was attributed to Na+ influx (I-Na) in nodes of Ranvier. The second one was blocked by 3,4-aminopyridine (3, 4-DAP) or tetraethylam monium (TEA), which corresponded to fast K+ outward current (I-K.F) th rough 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-sensit ive Ca2+-dependent K+ current (I-K(Ca)) passing through Ca2+ -activate d K+ channel was revealed, whose amplitude depended on [K+](0) and [Ca 2+](0). 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 beta-bungarotoxin ( 2 mu mol/L), and enhanced by low pH (6.4-6.7). This is the first repor t that certain current component of motor nerve terminal is sensitive to pH in the range of 6.4-7.5. (iv) That diazoxide (200 mu mol/L) incr eased the second negative peak and the effect was eliminated after fur ther addition of glibenclamide (50 mu mol/L) was taken as evidence for the presence of ATP-sensitive K+ current (I-K.ATP) at snake nerve ter minal.