In single guinea‐pig ventricular myocytes, we examined the stoichiometry of Na+‐Ca2+ exchange (NCX) by measuring the reversal potential (ENCX) of NCX current (INCX) and intracellular Ca2+ concentration ([Ca2+]i) with the whole‐cell voltage‐clamp technique and confocal microscopy, respectively. With given ionic concentrations in the external and pipette solutions, the predicted ENCX were −73 and −11 mV at 3:1 and 4:1 stoichiometries, respectively. ENCX measured were −69 ± 2 mV (n= 11), −47 ± 1 mV (n= 14) and −15 ± 1 mV (n= 15) at holding potentials (HP) of −73, −42 and −11 mV, respectively. Thus, ENCX almost coincided with HP, indicating that [Ca2+]i and/or [Na+]i changed due to INCX flow. Shifts of ENCX (ΔENCX) were measured by changing [Ca2+]o or [Na+]o. The measured values of ΔENCX were almost always smaller than those expected theoretically at a stoichiometry of either 3:1 or 4:1. Using indo‐1 fluorescence, [Ca2+]i measured under the whole‐cell voltage‐clamp supported a 3:1 but not 4:1 stoichiometry. To prevent Ca2+ accumulation, we inhibited INCX with Ni2+ and re‐examined ENCX during washing out Ni2+. With HP at predicted ENCX at a 3:1 stoichiometry, ENCX developed was close to predicted ENCX and did not change with time. However, with HP at predicted ENCX for a 4:1 stoichiometry, ENCX developed initially near a predicted ENCX for a 3:1 stoichiometry and shifted toward ENCX for a 4:1 stoichiometry with time. We conclude that the stoichiometry of cardiac NCX is 3:1.

The findings in this study showed substantial deterioration in clinical parameters related to lifestyle diseases and the presence of general psychological distress among residents living near the damaged nuclear power plant after the Fukushima Daiichi disaster. In addition to controlling the levels of radiation exposure, aggressive management of immediate physical and mental health crisis for residents may be necessary in future nuclear accidents.

Abstract. Using the whole-cell voltage clamp, we examined the mechanism of activation of the Na + / Ca 2+ exchanger (NCX) by hydrogen peroxide (H 2 O 2 ) in isolated guinea-pig cardiac ventricular myocytes. Exposure to H 2 O 2 increased the NCX current. The effect was inhibited by cariporide, an inhibitor of the Na + / H + exchanger (NHE), suggesting that there are NHEdependent and -independent pathways in the effect of H 2 O 2 on NCX. In addition, both pathways were blocked by edaravone, a hydroxyl radical (•OH) scavenger; pertussis toxin, a Gα i / o protein inhibitor; and U0126, an inhibitor of mitogen-activated protein kinase / extracellular signalregulated kinase kinase (MEK). On the other hand, wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, inhibited only the NHE-dependent pathway, while PP2, a Src family protein tyrosine kinase inhibitor, inhibited only the NHE-independent pathway. Taken together, our data suggest that H 2 O 2 increases the NCX current via two signal transduction pathways. The common pathway is the conversion of H 2 O 2 to •OH, which activates Gα i / o protein and a mitogen-activated protein (MAP) kinase signaling pathway. Then, one pathway activates NHE with a PI3K-dependent mechanism and indirectly increases the NCX current. Another pathway involves activation of a Src family tyrosine kinase.

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Abstract. The stoichiometry of the Na + / Ca 2+ exchanger (NCX) had been generally accepted as 3 Na + :1 Ca 2+ . However, recently a challenging stoichiometry of 4:1 was proposed. Therefore, using guinea pig ventricular cells, we re-examined the stoichiometry by measuring the reversal potential of the NCX current and intracellular Ca 2+ concentrations under the whole-cell voltage clamp. We confirmed that the stoichiometry of NCX is 3:1 not 4:1. In addition, we explored the possible reasons for obtaining erroneous results of a 4:1 stoichiometry.