Almers W, Stanfield P R, Stühmer W
J Physiol. 1983 Mar;336:261-84. doi: 10.1113/jphysiol.1983.sp014580.
We describe a method for recording Na+ and K+ currents (INa and IK) from small, voltage-clamped patches of sarcolemma by means of fire-polished glass micropipettes of 7-15 microns tip diameter. Recordings can be made successively from many areas of one fibre. On a given fibre, the amplitudes of INa and IK varied from point to point. Maximum Na+ current densities varied up to three-fold over distances of 10-30 microns, typically between 4 and 12 mA/cm2. K+ currents showed somewhat less lateral variation. Local densities of INa and IK showed no correlation. Apparently the density of Na+ (and, to a lesser extent, K+) channels varies laterally. A contour map of Na+ channel density is constructed for a 20 microns X 90 microns section of sarcolemma. Based on the steepness of lateral gradients in channel density and the estimated survival time of a Na+ channel, it is calculated that at least half of the Na+ channels have a lateral diffusion coefficient of less than 2 X 10(-12) cm2/s. This is three orders of magnitudes less than expected from their molecular size, and suggests that these channels are anchored in the sarcolemma.
我们描述了一种通过尖端直径为7 - 15微米的火抛光玻璃微电极，从电压钳制的小肌膜片记录Na⁺和K⁺电流（INa和IK）的方法。可以从一根纤维的多个区域连续进行记录。在给定的纤维上，INa和IK的幅度逐点变化。在10 - 30微米的距离上，最大Na⁺电流密度变化高达三倍，通常在4至12 mA/cm²之间。K⁺电流的横向变化略小。INa和IK的局部密度没有相关性。显然，Na⁺（以及在较小程度上K⁺）通道的密度在横向有所不同。构建了一个20微米×90微米肌膜切片的Na⁺通道密度等高线图。根据通道密度的横向梯度陡度和估计的Na⁺通道存活时间计算得出，至少一半的Na⁺通道横向扩散系数小于2×10⁻¹² cm²/s。这比根据其分子大小预期的值小三个数量级，表明这些通道锚定在肌膜中。
