ISSN:
1460-9568
Quelle:
Blackwell Publishing Journal Backfiles 1879-2005
Thema:
Medizin
Notizen:
A scorpion α-toxin-sensitive background sodium channel was characterized in short-term cultured adult cockroach dorsal unpaired median (DUM) neurons using the cell-attached patch-clamp configuration. Under control conditions, spontaneous sodium currents were recorded at different steady-state holding potentials, including the range of normal resting membrane potential. At –50 mV, the sodium current was observed as unclustered, single openings. For potentials more negative than –70 mV, investigated patches contained large unitary current steps appearing generally in bursts. These background channels were blocked by tetrodotoxin (TTX, 100 nm), and replacing sodium with TMA-Cl led to a complete loss of channel activity. The current–voltage relationship has a slope conductance of 36 pS. At –50 mV, the mean open time constant was 0.22 ± 0.05 ms (n = 5). The curve of the open probability versus holding potentials was bell-shaped, with its maximum (0.008 ± 0.004; n = 5) at –50 mV. LqhαIT (10–8m) altered the background channel activity in a time-dependent manner. At –50 mV, the channel activity appeared in bursts. The linear current–voltage relationship of the LqhαIT-modified sodium current determined for the first three well-resolved open states gave three conductance levels: 34, 69 and 104 pS, and reversed at the same extrapolated reversal potential (+52 mV). LqhαIT increased the open probability but did not affect either the bell-shaped voltage dependence or the open time constant. Mammal toxin AaHII induced very similar effects on background sodium channels but at a concentration 100 × higher than LqhαIT. At 10–7m, LqhαIT produced longer silence periods interrupted by bursts of increased channel activity. Whole-cell experiments suggested that background sodium channels can provide the depolarizing drive for DUM neurons essential to maintain beating pacemaker activity, and revealed that 10–7 m LqhαIT transformed a beating pacemaker activity into a rhythmic bursting.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1046/j.1460-9568.1999.00554.x
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