Intracellular calcium transients evoked by pulsed infrared radiation in neonatal cardiomyocytes.
Neonatal rat ventricular cardiomyocytes were used to investigate mechanisms underlying transient changes in intracellular free Ca2+ concentration ([Ca2+]i) evoked by pulsed infrared radiation (IR, 1862 nm). Fluorescence confocal microscopy revealed IR-evoked [Ca2+]i events with each IR pulse (3-4 ms pulse⁻¹, 9.1-11.6 J cm⁻² pulse⁻¹). IR-evoked [Ca2+]i events were distinct from the relatively large spontaneous [Ca2+]i transients, with IR-evoked events exhibiting smaller amplitudes (0.88 ΔF/F0 vs. 1.99 ΔF/F0) and shorter time constants (τ =0.64 s vs. 1.19 s, respectively). Both IR-evoked [Ca2+]i events and spontaneous [Ca2+]i transients could be entrained by the IR pulse (0.2-1 pulse s⁻¹), provided the IR dose was sufficient and the radiation was applied directly to the cell. Examination of IR-evoked events during peak spontaneous [Ca2+]i periods revealed a rapid drop in [Ca2+]i, often restoring the baseline [Ca2+]i concentration, followed by a transient increase in [Ca2+]i.Cardiomyocytes were challenged with pharmacological agents to examine potential contributors to the IR-evoked [Ca2+]i events. Three compounds proved to be the most potent, reversible inhibitors: (1) CGP-37157 (20 μM, n =12), an inhibitor of the mitochondrial Na+/Ca2+ exchanger (mNCX), (2) Ruthenium Red (40 μM, n =13), an inhibitor of the mitochondrial Ca2+ uniporter (mCU), and (3) 2-aminoethoxydiphenylborane (10 μM, n =6), an IP3 channel antagonist. Ryanodine blocked the spontaneous [Ca2+]i transients but did not alter the IR-evoked events in the same cells. This pharmacological array implicates mitochondria as the major intracellular store of Ca2+ involved in IR-evoked responses reported here. Results support the hypothesis that 1862 nm pulsed IR modulates mitochondrial Ca2+ transport primarily through actions on mCU and mNCX.
Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA. dittami@eng.utah.edu
Gregory M
GM
Dittami
Suhrud M
SM
Rajguru
Richard A
RA
Lasher
Robert W
RW
Hitchcock
Richard D
RD
Rabbitt
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism* / Q000528:radiation effects; D002478:Cells, Cultured; D005071:Evoked Potentials / Q000502:physiology* / Q000528:radiation effects; D006352:Heart Ventricles / Q000166:cytology / Q000378:metabolism / Q000528:radiation effects; D007259:Infrared Rays; D007424:Intracellular Fluid / Q000378:metabolism* / Q000528:radiation effects; D007834:Lasers; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000528:radiation effects; D051381:Rats; D017207:Rats, Sprague-Dawley
D002118:Calcium
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