Cell experiment:

EK 293 cells stably expressing the wtRyR1 (wtRyR1-HEK 293) are maintained in Dulbecco's modified Eagle's medium supplemented with 2 mM glutamine, 100 μg/mL streptomycin, 100 U/mL penicillin, 1 mM sodium pyruvate, and 10% fetal bovine serum at 37℃ under 5% CO2. wtRyR1-HEK 293 cells are loaded with 5 μM Fluo-4 acetoxymethyl ester at 37℃ for 30 min to measure Ca2+ transients in an imaging buffer consisting of 140 mM NaCl, 5 mM KCl, 2 mM MgCl2, 2 mM CaCl2, 10 mM HEPES, and 10 mM glucose, pH 7.4, supplemented with 0.05% bovine serum albumin. The cells are washed three times with imaging buffer and additionally incubated for 20 min at room temperature. Dye-loaded cells are washed three times with imaging buffer and imaged with a charge-coupled device camera with a 40× objective lens attached to an IX-71 microscope. The sequence of images is captured and monitored using EasyRatioPro. Caffeine dissolved in the imaging buffer is focally applied for 15 s using AutoMate Scientific. KB-R7943 is dissolved in the imaging buffer, and wtRyR1-HEK 293 cells are incubated for 10 min before the application of caffeine[2].

KB-R7943 mesylate is a potent and selective inhibitor of Na+/Ca2+ exchanger (NCE) with IC50 value of 0.7 μM.
NCE is an antiporter membrane protein that exchanges 3 Na+ for 1 Ca2+ and can function to cause Ca2+ accumulation (reverse mode) or Ca2+ extrusion (forward mode) depending on the concentrations of each ion on either side of the membrane and on the membrane potential [1].
In transfected Chinese hamster ovary (CHO) cells expressing NCE, KB-R7943 (10 μM) inhibited NCX activity at high (140mM) but not at low (10mM) cytosolic Na+ concentrations [2].
In cultured rat forebrain neurons loaded with glutamate- (3 μM), N-methyl-D-aspartate- (30 μM), kainate- (100 μM) or KCl- (50 mM) induced [Ca2+] transients, KBR7943 inhibited these transients with IC50 values of 6.6, 8.2, 5.2 and 2.9 μM, respectively. While, KB-R7943 didn't inhibit glutamate-induced neuronal injury [1]. In mice with ischemic acute renal failure (ARF), KB-R7943 significantly decreased endothelin-1 (ET-1) in the kidney and relieved the ARF-induced renal dysfunction [3].
References:
[1]. Hoyt KR, Arden SR, Aizenman E, et al. Reverse Na+/Ca2+ exchange contributes to glutamate-induced intracellular Ca2+ concentration increases in cultured rat forebrain neurons. Mol Pharmacol, 1998, 53(4): 742-749.
[2]. Condrescu M, Reeves JP. Inhibition of sodium-calcium exchange by KB-R7943: Dodecylamine and sphingosine in transfected Chinese hamster ovary cells. Cell Calcium, 2010, 47(5): 404-411.
[3]. Yamashita J, Ogata M, Takaoka M, et al. KB-R7943, a selective Na+/Ca2+ exchange inhibitor, protects against ischemic acute renal failure in mice by inhibiting renal endothelin-1 overproduction. J Cardiovasc Pharmacol, 2001, 37(3): 271-279.