Elevated maxi-K+ ion channel current in glaucomatous lamina cribrosa cells

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 Ca2+ entry channel inhibition (verapamil) and internal Ca2+ 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-ICE 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 Ca2+-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. (C) 2013 Published by Elsevier Ltd.