PHYSIOLOGICAL ROLE OF NEURONAL-GRIAL INTERACTION

Schwann cells were enzymatically isolated from squid giant axons。Macroscopic ionic currents were recorded using whole cell clamp and single channel currents using patch clamp。Two types of ionic currents were found with whole cell voltage clamp.One is voltage gated L-type calcium current sensitive to externally applied nifedipine or Co y D12文件D1.This current is activated at&gt；-40 mV。The other current is outwardly rectified potassium current。This current is blocked by externally applied nifedipine or CO I D12文件D1，but insensitive to externally applied caffeine，ryanodine or L-glutamate.Single potassium channel currents with a conductance of 40pS were recorded from excised inside-out patches。The open probability(Po)was 0.05 at 3 x 10 I D 1-7 I D 1 M Ca D 12 I D 1，increased transiently to 0.4 when the Ca I D 12 I D 1 concentration was elevated to 1×10 I D 1-6 I D 1 M，then ran down spontaneously at this Ca I D 12 I D 1 concentration.The channel activity was insensitive to externally applied L-glutamate，internally applied acetylcholine(ACh)，or ATP。The results suggest that the calcium activated potassium channels play an essential role in generation of the Schwann cell membrane potential of-40 mV，and the membrane potential is controlled by the intracellular Ca I D 12 ii D 1 level。Schwann cells were loaded fluo-3，a Ca I D12 I D 1-sensitive dye.Externally applied K induced an increase in the internal Ca I D12 I D 1 level only when external solution contained Ca I D 12 I D 1.Externally applied L-glutamate，ACh，and caffeine induced no detectable change in the internal Ca I D 12 I D 1 level.

Schwann cells were enzymatically isolated from squid giant axons. Macroscopic ionic currents were recorded using whole cell clamp and single channel currents using patch clamp. Two types of ionic currents were found with whole cell voltage clamp. One is voltage gated L-type calcium current sensitive to externally applied nifedipine or CoィイD12+ィエD1. This current is activated at >-40 mV. The other current is outwardly rectified potassium current. This current is blocked by externally applied nifedipine or COィイD12+ィエD1, but insensitive to externally applied caffeine, ryanodine or L-glutamate. Single potassium channel currents with a conductance of 40 pS were recorded from excised inside-out patches. The open probability (Po) was 0.05 at 3x10ィイD1-7ィエD1 M CaィイD12+ィエD1, increased transiently to 0.4 when the CaィイD12+ィエD1 concentration was elevated to 1×10ィイD1-6ィエD1 M, then ran down spontaneously at this CaィイD12+ィエD1 concentration. The channel activity was insensitive to externally applied L-glutamate, internally applied acetylcholine (ACh), or ATP. The results suggest that the calcium activated potassium channels play an essential role in generation of the Schwann cell membrane potential of -40 mV, and the membrane potential is controlled by the intracellular CaィイD12+ィエD1 level. Schwann cells were loaded fluo-3, a CaィイD12+ィエD1-sensitive dye. Externally applied K+ induced an increase in the internal CaィイD12+ィエD1 level only when external solution contained CaィイD12+ィエD1. Externally applied L-glutamate, ACh, and caffeine induced no detectable change in the internal CaィイD12+ィエD1level.