title: Four types of potassium currents in motor nerve terminals of snake.
abstract: The experiments were performed on transversus abdominis muscle of Elaphe dione by subendothelial recording. The results indicate that in snake motor nerve endings there exist four types of K(+) channels, i.e. voltage-dependent fast and slow K(+) channels, Ca(2+)-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(+) influx (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 [ca(2+) ](o). It was blocked by Ba(2+), Cd(2+) or Co(2+). (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 micromol/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 micromol/L) increased the second negative peak and the effect was eliminated after further addition of glibenclamide (50 micromol/L) was taken as evidence for the presence of ATP-sensitive K(+) current (I(K.ATP)) at snake nerve terminal.
authors: Shanghai Institute of Physiology, Chinese Academy of Sciences, China.
authors: Y
authors: Y
authors: Shi
authors: C
authors: C
authors: Gu
authors: Y
authors: Y
authors: Xu