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TOK homologue in Neurospora crassa : first cloning and functional characterisation of an ion channel in a filamentous fungus.

Roberts, Stephen K. (2003) TOK homologue in Neurospora crassa : first cloning and functional characterisation of an ion channel in a filamentous fungus. Eukaryotic Cell, 2 (1). pp. 181-190. ISSN 1535-9778

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Abstract

In contrast to animal and plant cells, very little is known of ion channel function in fungal physiology. The life cycle of most fungi depends on the "filamentous" polarized growth of hyphal cells; however, no ion channels have been cloned from filamentous fungi and comparatively few preliminary recordings of ion channel activity have been made. In an attempt to gain an insight into the role of ion channels in fungal hyphal physiology, a homolog of the yeast K+ channel (ScTOK1) was cloned from the filamentous fungus, Neurospora crassa. The patch clamp technique was used to investigate the biophysical properties of the N. crassa K+ channel (NcTOKA) after heterologous expression of NcTOKA in yeast. NcTOKA mediated mainly time-dependent outward whole-cell currents, and the reversal potential of these currents indicated that it conducted K+ efflux. NcTOKA channel gating was sensitive to extracellular K+ such that channel activation was dependent on the reversal potential for K+. However, expression of NcTOKA was able to overcome the K+ auxotrophy of a yeast mutant missing the K+ uptake transporters TRK1 and TRK2, suggesting that NcTOKA also mediated K+ influx. Consistent with this, close inspection of NcTOKA-mediated currents revealed small inward K+ currents at potentials negative of EK. NcTOKA single-channel activity was characterized by rapid flickering between the open and closed states with a unitary conductance of 16 pS. NcTOKA was effectively blocked by extracellular Ca2+, verapamil, quinine, and TEA+ but was insensitive to Cs+, 4-aminopyridine, and glibenclamide. The physiological significance of NcTOKA is discussed in the context of its biophysical properties.

Item Type: Article
Journal or Publication Title: Eukaryotic Cell
Subjects: Q Science > QH Natural history > QH301 Biology
Departments: Faculty of Health and Medicine > Biomedical & Life Sciences
ID Code: 9501
Deposited By: Dr Stephen K Roberts
Deposited On: 12 Jun 2008 11:47
Refereed?: Yes
Published?: Published
Last Modified: 26 Jul 2012 18:38
Identification Number:
URI: http://eprints.lancs.ac.uk/id/eprint/9501

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