Chloramine-T effect on sodium conductance of neuroblastoma cells as studied by whole-cell clamp and single-channel analysis.
Patch-clamp experiments were done on sodium channels of neuroblastoma cells (N1E-115) in the presence of tetraethylammonium ions to block potassium channels. In Ringer solution whole-cell records revealed a diphasic INa inactivation with the fast (tau 0) component. being clearly larger than the slow (tau 1 approximately 3 tau 0) component. In single-channel studies on inside-out patches the mean open time, to, turned out to be only a fraction of tau 0 and almost independent of membrane potential. After external application of chloramine-T INa inactivation of whole cells was delayed with both tau 0 and tau 1 increased, and incomplete, i.e. a persistent current component emerged. The latter was maximal at a more positive membrane potential than the peak current. Also, after chloramine-T treatment the peak INa increased, particularly at weak depolarizations. In inside-out patches the equally effective internal application of chloramine-T led to bursting channel openings with mean burst times (tb) approximately 6 ms, and gap times (tg) approximately 20 ms, where gap is defined as a closure of greater than or equal to 1.5 ms. Within the bursts to was approximately 2 ms, again clearly shorter than tau 0; the mean close time, tc was approximately 0.5 ms. The single-channel conductance was approximately 13 pS and unaffected by chloramine-T. Diphasic INa inactivation and the fact that to less than tau 0 led to an extension of the model of Aldrich and Stevens [J Neurosci 7:418-431 (1987)], in which overall kinetics is determined by the openings rather than closures of the sodium channels.(ABSTRACT TRUNCATED AT 250 WORDS)
Niemann
P
P
Physiologishes Institut, Universität Kiel, Federal Republic of Germany.
Schmidtmayer
J
J
Ulbricht
W
W
D002700:Chloramines / Q000494:pharmacology*; D004553:Electric Conductivity; D007552:Isotonic Solutions; D007700:Kinetics; D009447:Neuroblastoma / Q000378:metabolism; D000077331:Ringer's Solution; D012964:Sodium / Q000378:metabolism; D015222:Sodium Channels / Q000187:drug effects / Q000378:metabolism*; D014105:Tosyl Compounds; D014407:Tumor Cells, Cultured
D002700:Chloramines; D007552:Isotonic Solutions; D015222:Sodium Channels; D014105:Tosyl Compounds; C016300:chloramine-T; D000077331:Ringer's Solution; D012964:Sodium