Lateral distribution of sodium and potassium channels in frog skeletal muscle: measurements with a patch-clamp technique.
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.
D000818:Animals; D066298:In Vitro Techniques; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials; D009132:Muscles / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism* / Q000502:physiology; D011896:Rana temporaria; D012508:Sarcolemma / Q000502:physiology*; D012964:Sodium / Q000378:metabolism* / Q000502:physiology
D007473:Ion Channels; D012964:Sodium; D011188:Potassium