Abstract
We explore the feasibility of obtaining a spatially resolved picture of [Formula: see text] inward currents ([Formula: see text]) in multicellular cardiac tissue by differentiating optically recorded [Formula: see text] transients that accompany propagating action potentials. Patterned growth strands of neonatal rat ventricular cardiomyocytes were stained with the [Formula: see text] indicators Fluo-4 or Fluo-4FF. Preparations were stimulated at 1Hz, and [Formula: see text] transients were recorded with high spatiotemporal resolution ([Formula: see text], 2kHz analog bandwidth) with a photodiode array. Signals were differentiated after appropriate digital filtering. Differentiation of [Formula: see text] transients resulted in optically recorded calcium currents (ORCCs) that carried the temporal and pharmacological signatures of L-type [Formula: see text] inward currents: the time to peak amounted to [Formula: see text] (Fluo-4FF) and [Formula: see text] (Fluo-4), full-width at half-maximum was [Formula: see text], and ORCCs were completely suppressed by [Formula: see text][Formula: see text]. Also, and as reported before from patch-clamp studies, caffeine reversibly depressed the amplitude of ORCCs. The results demonstrate that the differentiation of [Formula: see text] transients can be used to obtain a spatially resolved picture of the initial phase of [Formula: see text] in cardiac tissue and to assess relative changes of activation/fast inactivation of [Formula: see text] following pharmacological interventions.
Highlights
When screening the past for methodological innovations that led to major advances in our understanding of the physiology of excitable tissues, neuroscientists have played a central role and their methodological work often spilled over into other scientific fields
Using a fast and highly sensitive optical recording system, we show in this study that the rising phase of Ca2þ transients accompanying propagated electrical activity in strands of cardiomyocytes stained with calcium indicators exhibits two phases: a fast rise within the first ∼5 ms and a slower rise to peak that is reached after an additional 20 to 30 ms
The spatiotemporal characteristics of Ca2þ transients accompanying action potential propagation were assessed in strands of cultured neonatal rat ventricular cardiomyocytes stained with Fluo-4
Summary
When screening the past for methodological innovations that led to major advances in our understanding of the physiology of excitable tissues, neuroscientists have played a central role and their methodological work often spilled over into other scientific fields This was the case for cardiac electrophysiology, where examples that led to major scientific advancements range from the invention of the Ling–Gerard– Graham glass electrode in the late 1940s1 to optical ion indicators and to optogenetics as introduced only a few years ago.[2] Being faced with the problem of assessing impulse propagation in networks of cultured cardiomyocytes with high spatiotemporal resolution in the early 1990s, the senior author of this study was yet another “specimen” of a cardiac electrophysiologist that had his hopes raised that the voltage-sensitive dye recording as developed by neuroscientists around Larry Cohen might solve the cardiac problem at hand.[3,4] As it turned out, during his 2-year stay in the laboratory of Brian Salzberg, a former collaborator of Larry Cohen in the voltage-sensitive dye development group, the technology transfer from neuroscience to cardiomyocyte cell cultures worked out just fine.[5,6,7] Getting to know Larry personally, had to wait until Brian’s lab went on its yearly summer trail to the MBL in Woods Hole. Once back in Switzerland, this input proved invaluable for the development of
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