Simultaneous maps of optical action potentials and calcium transients in guinea-pig hearts: mechanisms underlying concordant alternans.
1. The mechanisms underlying electro-mechanical alternans caused by faster heart rates were investigated in perfused guinea-pig hearts stained with RH237 and Rhod-2 AM to simultaneously map optical action potentials (APs) and intracellular free Ca2+ (Ca2+i). 2. Fluorescence images of the heart were focused on two 16 x 16 photodiode arrays to map Ca2+i (emission wavelength (lamdda;em) = 585 +/- 20 nm) and APs (lamdda;em > 715 nm) from 252 sites. Spatial resolution was 0.8 mm x 0.8 mm per diode and temporal resolution 4000 frames s-1. 3. The mean time-to-peak for APs and [Ca2+]i was spatially homogeneous (8.8 +/- 0.5 and 25.6 +/- 5.0 ms, respectively; n = 6). The durations of APs (APDs) and Ca2+i transients were shorter at the apex and progressively longer towards the base, indicating a gradient of ventricular relaxation. 4. Restitution kinetics revealed increasingly longer delays between AP and Ca2+i upstrokes (9.5 +/- 0.4 to 11.3 +/- 0.4 ms) with increasingly shorter S1-S2 intervals, particularly at the base, despite nearly normal peak [Ca2+]i. 5. Alternans of APs and Ca2+i transients were induced by a decrease++ in cycle length (CL), if the shorter CL captured at the pacing site and was shorter than refractory periods (RPs) near the base, creating heterogeneities of conduction velocity. 6. Rate-induced alternans in normoxic hearts were concordant (long APD with large [Ca2+]i) across the epicardium, with a magnitude (difference between odd-even signals) that varied with the local RP. Alternans were initiated by gradients of RP, producing alternans of conduction that terminated spontaneously without progressing to fibrillation.
Choi
B R
BR
Department of Cell Biology and Physiology, University of Pittsburgh, School of Medicine, Pittsburgh, PA 15261, USA.
Salama
G
G
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology; D002138:Calibration; D004558:Electric Stimulation; D004594:Electrophysiology; D005260:Female; D005456:Fluorescent Dyes; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology; D006339:Heart Rate / Q000502:physiology; D066298:In Vitro Techniques; D007700:Kinetics; D009206:Myocardium / Q000378:metabolism*; D009431:Neural Conduction / Q000502:physiology; D018408:Patch-Clamp Techniques; D012032:Refractory Period, Electrophysiological / Q000502:physiology; D013056:Spectrophotometry, Ultraviolet
D015220:Calcium Channels; D005456:Fluorescent Dyes