Kinetic separation of charge movement components in intact frog skeletal muscle.
1. Procedures for a complete charge movement separation employed a combination of its steady-state inactivation and activation properties in intact frog skeletal muscle fibres in gluconate-containing solutions. 2. Holding potential shifts from -70 to -50 mV reduced the total charge available between -90 and -20 mV from 16.76 +/- 1.70 nC microF-1 (mean +/- S.E.M.; n = 4 fibres) to 9.25 +/- 1.43 nC microF-1 without significant loss of tetracaine-resistant charge (q beta). 3. The steady-state and kinetic properties of tetracaine-sensitive charge (q gamma) persisted through holding potential changes from -90 to -70 mV in the presence of gluconate and generally resembled activation properties established hitherto in sulphate-containing solutions. 4. Further holding potential displacement to -50 mV abolished q gamma charge movements and depressed the charge-voltage curve. 5. Test voltage steps applied from a -70 mV prepulse level gave rapid monotonic q beta decays and similarly depressed activation functions in 2 mM tetracaine unchanged by holding potential shifts between -70 and -50 mV. 6. The isolated 'on' q gamma charge movements, I(t), always included early transients that preceded any prolonged charging phases and which increased with depolarization. They decayed to stable baselines in the absence of prolonged time-dependent or inward-current phases and yielded integrals, Q(t), that monotonically increased with test voltage. 7. 'Off' steps always elicited rapid monotonic q gamma decays that fully returned the 'on' charge. 8. 'On' and 'off' q gamma currents, I(t), following voltage steps from fixed conditioning to varying test levels mapped onto topologically distinct higher-order phase-plane trajectories, I(Q), that steeply varied with test voltage. 9. In contrast, voltage steps to fixed test potentials of either -70 or -20 mV elicited identical q gamma phase-plane trajectories independent of prepulse history. 10. The q gamma current thus reflects an independent, capacitative process driven uniquely by higher-order dependences upon charge distribution, Q(t), and test voltage, V(t), autonomous of prepulse history or time, t.
Huang
C L
CL
Physiological Laboratory, Cambridge, UK.
D000818:Animals; D005942:Gluconates / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects; D018482:Muscle, Skeletal / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D011896:Rana temporaria; D013748:Tetracaine / Q000494:pharmacology
D005942:Gluconates; D013748:Tetracaine; C030691:gluconic acid