INTRAMEMBRANOUS CHARGE MOVEMENT IN FROG CUT TWITCH FIBERS MOUNTED IN A DOUBLE VASELINE-GAP CHAMBER

Intramembranous charge movement was measured in cut twitch fibers mounted in a double Vaseline-gap chamber with either a tetraethylammonium chloride (TEA · Cl) or a TEA2 · S04 solution (13-14°C) in the central pool. Charge vs. voltage data were fitted by a single two-state Boltzmann distribution function. The average values of V (the voltage at which steady-state charge is equally distributed between the two Boltzmann states), k (the voltage dependence factor), and qmaxcm (the maximum charge divided by the linear capacitance, both per unit length of fiber) were V = -53.3 mV (SEM, 1.1 mV), k = 6.3 mV (SEM, 0.3 mV), qmaxcm = 18.0 nC/µF (SEM, 1.1 nC/µF) in the TEA · Cl solution; and V = -35.1 mV (SEM, 1.8 mV), k = 10.5 mV (SEM, 0.9 mV), qmax/cm 36.3 nC/µF (SEM, 3.2 nC/µF) in the TEA2 · SO4 solution. These values of k are smaller than those previously reported for cut twitch fibers and are as small as those reported for intact fibers. If a correction is made for the contributions of currents from under the Vaseline seals, V = -51.2 mV (SEM, 1.1 mV), k = 7.2 mV (SEM, 0.4 mV), qmaxcm = 22.9 nC/µF (SEM, 1.4 nC/µF) in the TEA · Cl solution; and V = -34.0 mV (SEM, 1.9 mV), k = 10.1 mV (SEM, 1.1 mV), qmax/cm = 38.8 nC/µF (SEM, 3.2 nC/µF) in the TEA2 · SO4 solution. With this correction, however, the fit of the theoretical curve to the data is poor. A good fit with this correction can be obtained with a sum of two Boltzmann distribution functions. The first has average values V = -33.0 mV (SEM, 2.8 mV), k = 11.0 mV (SEM, 0.5 mV), 9max/cm = 10-6 nC/µF (SEM, 1.0 nC/µF) in the TEA · Cl solution; and V = -20.0 mV (SEM, 3.3 mV), k = 17.0 mV (SEM, 2.0 mV), qmaxcm = 36.4 nC/µF (SEM, 2.3 nC/µF) in the TEA2 · SO4 solution. The second has average values V = -56.5 mV (SEM, 1.3 mV), k = 2.9 mV (SEM, 0.4 mV), qmaxcm = 13.2 nC/µF (SEM, 1.0 nC/µF) in the TEA · C1 solution; and V = -41.6 mV (SEM, 1.4 mV), k - 2.5 mV (SEM, 0.8 mV), qmax/cm = 11.8 nC/µF (SEM, 1.7 nC/µF) in the TEA2 · SO4 solution. When a fiber is depolarized to near V of the second Boltzmann function, a slowly developing "hump" appears in the ON-segment of the current record. These results show that a steeply voltage-dependent component of charge, with properties similar to those of Qr charge in intact fibers (Adrian, R.H., and A. Peres. 1979. Journal of Physiology. 289:83-97), can be clearly resolved in cut fibers. © 1990, Rockefeller University Press., All rights reserved.