Sodium-calcium exchange influences the response to endothelin-1 in lens epithelium.
Studies were conducted to examine the possible involvement of Na+-Ca2+ exchanger in determining the magnitude of the endothelin-1 (ET-1)-receptor-mediated calcium signal in porcine lens epithelial cells. Cytoplasmic calcium concentration was measured in primary cultured cells loaded with Fura-2. ET-1 (100 nM) caused cytoplasmic calcium to increase transiently to approximately 250 nM from a baseline of approximately 65 nM. The calcium increase decayed to a sustained plateau 35-45 nM above the baseline. Both the peak and plateau component of the ET-1 calcium response were abolished by PD145065, an ET receptor antagonist, and by cyclopiazonic acid (CPA) (10 microM). In calcium-free bathing solution, only the plateau was abolished. In the presence of ouabain, low-sodium bathing solution or bepridil, a sodium-calcium exchange inhibitor, peak height more than doubled. Bepridil also increased the peak height of the calcium response to ATP. The half-time for decay of the ET-1 and ATP calcium peak was increased several folds by bepridil, ouabain and low-sodium conditions. Measurements of ionomycin-releasable calcium suggested calcium store size was not increased in bepridil-treated cells. Taken together findings suggest inhibition of sodium-calcium exchange increases the magnitude of the receptor-initiated store-release phase of the ET-1 calcium signaling response as the result of impaired calcium clearance from the cytoplasm.
Okafor
Mansim
M
Department of Ophthalmology and Visual Sciences, School of Medicine, University of Louisville, Louisville, KY 40202, USA.
Tamiya
Shigeo
S
Delamere
Nicholas A
NA
D000818:Animals; D015764:Bepridil / Q000494:pharmacology; D015153:Blotting, Western; D002118:Calcium / Q000032:analysis / Q000378:metabolism; D020013:Calcium Signaling / Q000502:physiology*; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors; D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1 / Q000494:pharmacology / Q000502:physiology*; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D016257:Fura-2 / Q000032:analysis / Q000378:metabolism; D007150:Immunohistochemistry; D007211:Indoles / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007908:Lens, Crystalline / Q000187:drug effects / Q000502:physiology*; D008856:Microscopy, Fluorescence; D009842:Oligopeptides / Q000494:pharmacology; D010042:Ouabain / Q000494:pharmacology; D044022:Receptor, Endothelin A / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D019831:Sodium-Calcium Exchanger / Q000032:analysis / Q000502:physiology*; D013552:Swine
D065130:Endothelin A Receptor Antagonists; D019332:Endothelin-1; D007211:Indoles; D009842:Oligopeptides; D044022:Receptor, Endothelin A; D019831:Sodium-Calcium Exchanger; C082887:PD 145065; D015759:Ionomycin; D010042:Ouabain; D015764:Bepridil; D012964:Sodium; D000252:Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2; C000543:cyclopiazonic acid