title: Elevated maxi-K(+) ion channel current in glaucomatous lamina cribrosa cells.
abstract: The connective tissue plates of the lamina cribrosa (LC) region are continuously exposed to a mechanically dynamic environment. To study how the LC cells respond to these mechanical forces, we measured the mechano-sensitive calcium dependent maxi-K(+) ion channel current in the cell membrane of LC cells of glaucoma and normal subjects. Primary culture LC cells from 7 normal and 7 age matched glaucoma donors were studied. Perfusion of cells with hypotonic solution was used to stretch the cell membrane. Whole-cell patch-clamp technique was used to measure the basal (non stretched) and hypotonic stretch-induced changes in maxi-K(+) ion channel activity in normal and glaucoma LC cells. The role of membrane-type Ca(2+) entry channel inhibition (verapamil) and internal Ca(2+) store re-uptake blockade (2-APB) on maxi-K(+) activity was also examined. Basal and stretched-induced maxi-K(+) current were significantly elevated in the glaucoma LC cells compared to normal controls (p < 0.05). In normal LC cells hypotonic stretch elevated the mean maxi-K(+) current from 18.5 ± 5.7 pA/pF (at Vp = +100 mV) to 88.4 ± 12.4 pA/pF (P < 0.05), and from 39.5 ± 7.3 pA/pF to 133.1 ± 18.5 pA/pF in glaucoma LC cells (P < 0.02). Verapamil and 2-APB significantly reduced basal maxi-K(+) current in glaucoma LC cells (33.1 ± 8.2 pA/pF to 17.9 ± 5.6 pA/pF; and 32.2 ± 8.3 pA/pF to 17.3 ± 5.4 pA/pF, P < 0.05, respectively) but not in normal LC cells (P > 0.05). Following hypotonic stretch, verapamil and 2-APB significantly (P < 0.05) reduced the maxi-K(+) current in both normal and glaucoma LC cells. Baseline and hypotonic stretch induced Ca(2+)-dependent maxi-K(+) channel activity are elevated in LC cells of glaucoma patients, which may result from the abnormally high levels of intracellular calcium in glaucoma LC cells.
authors.affiliation: UCD School of Medicine and Medical Science, University College Dublin, Ireland.
authors.forename: Mustapha
authors.initials: M
authors.lastname: Irnaten
authors.forename: Richard C
authors.initials: RC
authors.lastname: Barry
authors.forename: Deborah M
authors.initials: DM
authors.lastname: Wallace
authors.forename: Neil G
authors.initials: NG
authors.lastname: Docherty
authors.forename: Barry
authors.initials: B
authors.lastname: Quill
authors.forename: Abbot F
authors.initials: AF
authors.lastname: Clark
authors.forename: Colm J
authors.initials: CJ
authors.lastname: O'Brien
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001896:Boron Compounds / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D005901:Glaucoma / Q000378:metabolism*; D006801:Humans; D007038:Hypotonic Solutions; D051036:Large-Conductance Calcium-Activated Potassium Channels / Q000378:metabolism*; D009898:Optic Disk / Q000187:drug effects / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D012590:Sclera / Q000187:drug effects / Q000378:metabolism*; D014019:Tissue Donors; D014700:Verapamil / Q000494:pharmacology
chemical_list: D001896:Boron Compounds; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D007038:Hypotonic Solutions; D051036:Large-Conductance Calcium-Activated Potassium Channels; D014700:Verapamil; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium
keywords: fibrosis; glaucoma; lamina cribrosa; maxi-k(+)