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“Window” current in voltage gated calcium channels
Author(s) -
Easton Alice,
Bartlett Robert,
Souvannakitti Dangjai,
Hanck Dorothy A.
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.5.a538-b
Subject(s) - membrane potential , biophysics , voltage dependent calcium channel , voltage gated ion channel , calcium , chemistry , patch clamp , t type calcium channel , calcium channel , extracellular , electrophysiology , hek 293 cells , flux (metallurgy) , ion channel , biology , neuroscience , biochemistry , receptor , organic chemistry
T‐type calcium channels exhibit persistent activity over a physiologically relevant voltage range near the resting potential (“window”). The true extent is difficult to estimate electrophysiologically, and we, therefore, created cell lines expressing T‐type channels or L‐type channels in sufficient numbers to study Ca 2+ flux and inwardly rectifying K channels to control potential. We determined the relationship of membrane potential to Ca 2+ flux using a FURA‐2 based assay and perforated patch to measure resting membrane potentials in different extracellular K + concentrations for HEK293 parent cells and various stable lines expressing different channel densities. Adherent parent HEK293 cells expressed greater numbers of K channels than cells released from the dish. We identified cell lines in which K channel density was sufficient to hold membrane potential in the face of changes in calcium channel open probability and we could, therefore, establish the relationship between calcium channel open probability and flux. Not only can these cell lines establish the extent of the window current, but they can be helpful in evaluating the voltage dependence of calcium channel modifiers and drugs. AE was an APS Undergraduate Summer Research Fellow and RB was an APS Frontiers in Physiology fellow.