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Voltage-clamp studies were carried out to compare currents through Ca2+ channels (ICa) with Na+ currents (Ins) through a non-selective cation conductance blocked by micromolar concentrations of external Ca2+. The gating of both currents was found to have similar time and voltage dependence. The amplitudes of ICa and Ins varied widely, but Ins was always(More)
As a final step in endocytosis, clathrin-coated pits must separate from the plasma membrane and move into the cytosol as a coated vesicle. Because these events involve minute movements that conventional light microscopy cannot resolve, they have not been observed directly and their dynamics remain unexplored. Here, we used evanescent field (EF) microscopy(More)
Using flash photolysis of caged Ca2+ and the membrane capacitance to monitor exocytosis, we have studied the response of single melanotrophs to a step rise in cytosolic Ca2+ concentration ([Ca2+]i). Exocytosis begins with a rapid burst. This burst is followed by a slower phase, which is inhibited at cytosolic pH 6.2, and an ultraslow phase, which is(More)
1. Ca2+ currents in frog skeletal muscle fibres were studied with a voltage-clamp technique. Under membrane depolarization maintained for several seconds, Ca2+ current was found to decline with time constants of 0.2-2 sec when [Ca2+]o = 10 mM. 2. Ca2+ currents are diminished by nifedipine, D-600, tetracaine and Ni2+. 3. When peak current is diminished by(More)
Membrane currents were recorded from voltage-clamped, EGTA-loaded muscle fibres under conditions where currents through ordinary Na+, K+ and Cl- channels were prevented by drugs or by absence of permeant ions (K+, and Cl-). At 10 mM-external [Ca2+], substitution of Na+ for the large and presumably impermeant organic cations tetramethyl- (TMA+) or(More)
In mast cells and granulocytes, exocytosis starts with the formation of a fusion pore. It has been suggested that neurotransmitters may be released through such a narrow pore without full fusion. However, owing to the small size of the secretory vesicles containing neurotransmitter, the properties of the fusion pore formed during Ca2+-dependent exocytosis(More)
The permeability of Ca channels to various foreign cations has been investigated in the absence of external Ca2+. All physiological metal cations are clearly permeant, including Mg2+. The large organic cation n-butylamine+ is sparingly permeant or impermeant, but its larger derivative 1,4-diaminobutane2+ is highly permeant. Among the cations of the(More)
To sustain high rates of transmitter release, synaptic terminals must rapidly re-supply vesicles to release sites and prime them for exocytosis. Here we describe imaging of single synaptic vesicles near the plasma membrane of live ribbon synaptic terminals. Vesicles were captured at small, discrete active zones near the terminal surface. An electric(More)
A voltage clamp technique was used to study sodium currents and gating currents in squid axons internally perfused with the membrane impermeant sodium channel blocker, QX-314. Block by QX-314 is strongly and reversibly enhanced if a train of depolarizing pulses precedes the measurement. The depolarization-induced block is antagonized by external sodium.(More)