Fig. 3.
Multiple components of whole-cell VGKC revealed by inactivation kinetics. A, A cell with obviousIA was selected for this example. Whole-cell VGKC was elicited during a 200 msec step to 30 mV from −100 mV, as shown in the inset. The current amplitude was digitized and put in a LOG coordinate. The late part, but not the early part, of the current displayed a linear relationship with a time constant of 250 msec. This linear relationship was then extrapolated forward and subtracted from the early part of the digitized current, which resulted in another linear relationship with a time constant of 15 msec. This exponential peeling of decay within the time course demonstrated two components (n = 7).B, Whole-cell VGKC was elicited during a longer (4 sec) step to 30 mV from −100 mV, as shown in the inset. Exponential peeling of the components of decay of this trace revealed two time constants of 200 msec and 2.9 sec (n = 6).C, Whole-cell VGKC was elicited during a 40 sec step to 30 mV from −100 mV, as shown in the inset. Exponential peeling of the components of decay of this trace revealed two time constants of 3.4 and 25 sec (n = 3).D, A protocol as shown in the inset was used to elicit the K+ tail current. Exponential fitting revealed two components in the tail current (using the 40 mV step as the example) with time constants of 8 and 43 msec (n = 4). Taken together, these data support four distinct inactivation time constants, one consistent withIA, one consistent withIK, and two as distinct components ofID.