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Photoresponsive ion extraction/release systems: dynamic ion optodes for calcium and sodium based on photochromic spiropyran.

ABSTRACT: Photoresponsive ion extraction/release systems (PRIONERS) represent a highly interesting tool for the localized and time-controlled chemical perturbation of biological materials. We report here on our first results on phototriggered calcium and sodium exchanging materials. Such materials exist in two distinct states ("on" and "off"), depending on the wavelength of illumination. We used a combination of spectroscopic and electrochemical methods to obtain a better understanding of the dynamic processes involved in the triggered ion-exchange reaction upon activation of the photoactive compound. The driving force for the ion exchange is the light-induced acidity change of the chromoionophore. Activation with UV light generates a species in the membrane with an increased pKa. Protons are pulled into the membrane, and at the same time, ions are expelled. The selectivity of the system is determined by the employed ionophore. In contrast to photoresponsive ionophore-based systems, the concept presented here is applicable for virtually any ion of interest for which an ionophore exists.

SUBMITTER: Mistlberger G

PROVIDER: S-EPMC3589883 | biostudies-other | 2013 Mar

REPOSITORIES: biostudies-other

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Photoresponsive ion extraction/release systems: dynamic ion optodes for calcium and sodium based on photochromic spiropyran.

Mistlberger Günter G Xie Xiaojiang X Pawlak Marcin M Crespo Gastón A GA Bakker Eric E

Analytical chemistry 20130222 5

Photoresponsive ion extraction/release systems (PRIONERS) represent a highly interesting tool for the localized and time-controlled chemical perturbation of biological materials. We report here on our first results on phototriggered calcium and sodium exchanging materials. Such materials exist in two distinct states ("on" and "off"), depending on the wavelength of illumination. We used a combination of spectroscopic and electrochemical methods to obtain a better understanding of the dynamic proc ...[more]

PMID: 23387291

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Project description:In cardiac myocytes, excitation-contraction coupling depends upon sarcoplasmic reticular Ca2+ release triggered by Ca2+ influx through L-type Ca2+ channels. Although Na+-Ca2+ exchange (NCX) is essential for Ca2+ extrusion, its participation in the trigger process of excitation-contraction coupling is controversial. To investigate the role of NCX in triggering, we examined Ca2+ sparks in ventricular cardiomyocytes isolated from wild-type (WT) and cardiac-specific NCX knockout (KO) mice. Myocytes from young NCX KO mice are known to exhibit normal resting cytosolic Ca2+ and normal Ca2+ transients despite reduced L-type Ca2+ current. We loaded myocytes with fluo-3 to image Ca2+ sparks using confocal microscopy in line-scan mode. The frequency of spontaneous Ca2+ sparks was reduced in KO myocytes compared with WT. However, spark amplitude and width were increased in KO mice. Permeabilizing the myocytes with saponin eliminated differences between spontaneous sparks in WT and KO mice. These results suggest that sarcolemmal processes are responsible for the reduced spark frequency and increased spark width and amplitude in KO mice. When myocytes were loaded with 1 mM fluo-3 and 3 mM EGTA via the patch pipette to buffer diadic cleft Ca2+, the number of sparks triggered by action potentials was reduced by 60% in KO cells compared to WT cells, despite similar SR Ca2+ content in both cell types. When EGTA was omitted from the pipette solution, the number of sparks triggered in KO and WT myocytes was similar. Although the number of sparks was restored in KO cells, Ca2+ release was asynchronous. These results suggest that high subsarcolemmal Ca2+ is required to ensure synchronous triggering with short spark latency in the absence of NCX. In WT mice, high subsarcolemmal Ca2+ is not required for synchronous triggering, because NCX is capable of priming the diadic cleft with sufficient Ca2+ for normal triggering, even when subsarcolemmal Ca(2+) is lowered by EGTA. Thus, reducing subsarcolemmal Ca2+ with EGTA in NCX KO mice reveals the dependence of Ca2+ release on NCX.

Dataset Information

Photoresponsive ion extraction/release systems: dynamic ion optodes for calcium and sodium based on photochromic spiropyran.

Publications

Photoresponsive ion extraction/release systems: dynamic ion optodes for calcium and sodium based on photochromic spiropyran.

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