ISSN:
1432-1424
Keywords:
Fura 2
;
Fluorescent imaging
;
Cornea
;
Epithelia
;
Calcium conductance
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract We performed experiments to elucidate the calcium influx pathways in freshly dispersed rabbit corneal epithelial cells. Three possible pathways were considered: voltage-gated Ca++ channels, Na+/Ca++ exchange, and nonvoltage-dependent Ca++-permeable channels. Whole cell inward currents carrying either Ca++ or Ba++ were not detected using voltage clamp techniques. We also used imaging technology and the Ca++-sensitive ratiometric dye fura 2 to measure changes in intracellular Ca++ concentration ([Ca]i). Bath perfusion with NaCl Ringer's solution containing the calcium channel agonist Bay-K-8644 (1 μm), or Ni++ (40 μm), a blocker of many voltage-dependent calcium channels, did not affect [Ca++]i. Membrane depolarization with a KCl Ringer's bath solution resulted in a decrease in [Ca++]i. These results are inconsistent with the presence of voltage gated Ca++ channels. Nonvoltage gated Ca++ entry, on the other hand, would be reduced by membrane depolarization and enhanced by membrane hyperpolarization. Agents which hyperpolarize via stimulation of K+ current, such as flufenamic acid, resulted in an increase in ratio intensity. The cells were found to be permeable to Mn++ and bath perfusion with 5 mm Ni++ decreased [Ca++]i suggesting that the Ca++ conductance was blocked. These results are most consistent with a nonvoltage gated Ca++ influx pathway. Finally, replacing extracellular Na+ with Li+ resulted in an increase in [Ca++]i if the cells were first Na+-loaded using the Na+ ionophore monensin and ouabain, a Na+-K+-ATPase inhibitor. These results suggest that Na+/Ca++ exchange may also regulate [Ca++] in this cell type.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00232803
