Kinetics and steady-state properties of the charged system controlling sodium conductance in the squid giant axon.

摘要: 1. Asymmetries in the early time course of displacement current passing across membrane after application equal voltage-clamp pulses two directions have been investigated squid giant axon. Before making measurements, Na was blocked by removal external and treatment with tetrodotoxin. Potassium usually perfusion CsF, but some experiments were done intact axons. A signal averaging technique used to eliminate symmetrical components current.2. The asymmetrical had a contribution appreciable size attributed movement mobile charges or dipoles membrane. This manifested as an outward rising rapidly peak on depolarization then declining exponentially zero, followed at end pulse inward surge similar course. There also sustained flow outwards during pulse, arising from ionic leakage rectifying characteristic.3. identification changing component charged particles forming integral part supported demonstration that total transfer charge opposite beginning it reached saturation when internal potential taken sufficient positive value, its unaffected temperature, although constant large temperature coefficient.4. disposition steady state shown obey Boltzmann distribution. At midpoint distribution curve, proportion displaced underwent e-fold change for 19 mV potential. effective valency particles, is their actual multiplied fraction electric field acting them, therefore 1.3.5. quantity estimated about 1500 x 10(-12) C 0.05 cm(2) membrane, corresponding 1900 charges/mum(2).6. these gating responsible controlling conductance findings (a) constants same those Hodgkin & Huxley's ;m' system, both absolute magnitude dependence (b) transition which evenly distributed sides agreed system axons, value similarly shifted direction reduction strength raising Ca concentration, (c) comparison steepness curves governing one hand steady-state other conductance, suggested cooperation groups three involved, again excellent agreement system.7. Displacement pH over range 5-8, preliminary observations showed 1% procaine reduced somewhat less than 40% initial roughly halved constant.