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W F Gilly

Publications and source records attributed to W F Gilly.

43 records · Page 3Linked to original sources
PubMed1980

Voltage-dependent charge movement in frog slow muscle fibres.

1. Voltage-clamp experiments on frog slow and twitch fibres were carried out using the three-micro-electrode technique. Potassium currents were blocked by tetraethylammonium. Contraction was blocked by 2 mM-tetracaine. 2. After subtracting the linear capacitive and leakage currents, the delta V(test-control) traces from slow fibres show 'on' and 'off' charge movements similar to those observed in twitch fibres. 3. The time integrals of the 'on' and 'off' transients, Qon and Qoff, in slow fibres are, as in twitch fibres, almost equal in magnitude but opposite in direction. 4. The charge-voltage distribution is well fitted by a sigmoid curve given by (Formula: see text), which has been successfully applied to twitch fibres. Data from three fibres gave V = -25 mV, k = 13 mV, and Qmax = 7 nC/microF. Thus, intramembranous charge in slow fibres has the same steady-state voltage distribution as that in twitch fibres, but the quantity of maximum movable charge is only 1/4 to 1/3 as large. 5. Charge movement in slow fibres does not inactivate completely when the fibres are held at -20 to 0 mV for durations as long as 30 min. 6. These results show that charge movement exists in slow fibres and may serve the same function in regulating contractile activation as that postulated for twitch fibres. The lack of complete inactivation may be consistent with the ability of slow fibres to maintain maximal tension during prolonged depolarizations.

Animals↗
PubMed1979

Fast and slow steps in the activation of sodium channels.

Kinetic features of sodium conductance (gNa) and associated gating current (Ig) were studied in voltage-clamped, internally perfused squid axons. Following a step depolarization Ig ON has several kinetic components: (a) a rapid, early phase largely preceding gNa turn-on; (b) a delayed intermediate component developing as gNa increases; and (c) a slow component continuing after gNa is fully activated. With small depolarizations the early phase shows a quick rise (less than 40 mus) and smooth decay; the slow component is not detectable. During large pulses all three components are present, and the earliest shows a rising phase or initial plateau lasting approximately 80 mus. Steady-state and kinetic features of Ig are minimally influenced by control pulse currents, provided controls are restricted to a sufficiently negative voltage range. Ig OFF following a strong brief pulse also shows a rising phase. A depolarizing prepulse producing gNa inactivation and Ig immobilization eliminates the rising phase of Ig OFF. gNa, the immobilized portion of Ig ON, and the rising phase reappear with similar time-courses when tested with a second depolarizing pulse after varying periods of repolarization. 30 mM external ZnCl2 delays and slows gNa activation, prolongs the rising phase, and slows the subsequent decay of Ig ON. Zn does not affect the kinetics of gNa tails or Ig OFF as channels close, however. We present a sequential kinetic model of Na channel activation, which adequately describes the observations. The rapid early phase of IgON is generated by a series of several fast steps, while the intermediate component reflects a subsequent step. The slow component is too slow to be clearly associated with gNa activation.

Animals↗
PubMed1975

Slow fibers in the frog cruralis muscle.

Extrafusal slow fibers have been identified by electron microscopy in a muscle fiber bundle isolated from the anterior head (m. cruralis) of the triceps femoris of Rana pipiens. Light microscopic examination of this muscle revealed two equally numerous fiber types, one Fibrillenstruktur-like (twitch) and the other structureless (slow). A comparison of force developed by tetanic stimulation and by K+ depolarization also suggested approximately equal numbers of twitch and slow fibers.

Animals↗
PubMedDate not supplied

Threshold channels--a novel type of sodium channel in squid giant axon.

Sodium channels in nerve and muscle cells are functionally similar across wide phylogenetic boundaries and are usually thought to represent a single, homogeneous population that initiates the action potential at threshold and unerringly transmits it along the surface membrane. In marked contrast, many cell types are known to have several distinct potassium permeability systems. Distinguishable populations of Na channels have been reported in a few cell types, however, including denervated skeletal muscle, embryonic cardiac muscle, Purkinje cell somata and non-myelinated axons at low temperature. We report here that in squid giant axon, in standard experimental conditions, there are two functionally distinct populations of Na channels. The newly discovered population accounts for only a few per cent of the total Na permeability. The channels are selectively activated by small depolarizations and have very slow closing kinetics. Because these channels activate at voltages near the resting potential and tend to stay open for long times, they must dominate behaviour of the axon membrane in the threshold region for action potential initiation.

Animals↗
PubMedDate not supplied

Identified ion channels in the squid nervous system.

Our modern understanding of channels as discrete voltage-sensitive and ion-selective entities comes largely from a series of classical studies using the squid giant axon. This system has also been critical for understanding how transporters and synaptic transmission operate. This review outlines attempts to assign molecular identities to the extensively studied physiological properties of this system. As it turns out, this is no simple task. Molecular candidates for voltage-gated Na(+), K(+), and Ca(2+) channels, as well as ion transporters have been isolated from the squid nervous system. Both physiological and molecular approaches have been used to equate these cloned gene products with their native counterparts. In the case of the delayed rectifier K(+) conductance, the most thoroughly studied example, two major issues further complicate the equation. First, the ability of K(+) channel monomers to form heteromultimers with unique properties must be considered. Second, squid K(+) channel mRNAs are extensively edited, a process that can generate a wide variety of channel proteins from a common gene. The giant axon system is beginning to play an important role in understanding the biological relevance of this latter process.

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