Buffering of calcium influx by sarcoplasmic reticulum during the action potential in guinea‐pig ventricular myocytes.
Population
Guinea-pig single ventricular myocytes
Comparison
Rapid, brief pulses of caffeine, electrical… vs Electrical stimulation alone or voltage clamp…
Design
Preclinical
Authors
Discussion
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Implication
Supports SR buffering of Ca influx in ventricular myocytes; hypothesis-generating for cardiac Ca2+ handling, leaves open human translation.
Key Points
- To determine whether and to what extent trans-sarcolemmal calcium influx during cardiac depolarization is immediately sequestered by the sarcoplasmic reticulum.
- Monitored intracellular calcium transients using indo-1 fluorescence and measured twitch contractions elicited by action potentials, voltage-clamp pulses, or rapid caffeine applications in isolated guinea-pig ventricular myocytes (n=21).
- Depleted sarcoplasmic reticulum calcium stores with rapid, brief (100–200 ms) caffeine pulses or pharmacological inhibitors (100 nM ryanodine or 200 nM thapsigargin).
- Evaluated the effect of caffeine pulse application during depolarizing steps on whole-cell L-type calcium currents (ICa) using patch-clamp electrophysiology.
- In sarcoplasmic reticulum-depleted myocytes, simultaneous caffeine application and electrical stimulation increased the rate of rise by 53 ± 8% and the transient amplitude by 63 ± 9% (mean ± SEM, n=21) compared to electrical stimulation alone.
- Caffeine application during depolarizing voltage-clamp steps accelerated inactivation and decreased or left unchanged peak L-type calcium current, resulting in reduced total calcium influx.
- The enhancement of calcium transients despite reduced L-type calcium influx indicates that the sarcoplasmic reticulum actively and rapidly buffers a portion of incoming calcium during depolarization.
Structured PICO
P
Population
Guinea-pig single ventricular myocytes
I
Intervention
Rapid, brief (100-200 ms) pulses of caffeine, electrical stimulation, and voltage clamp pulses, with or without SR inhibitors (ryanodine 100 nM or thapsigargin 200 nM)
C
Comparator
Electrical stimulation alone or voltage clamp alone in cells with Ca2+-depleted sarcoplasmic reticulum
O
Outcome
Intracellular [Ca2+] transients (measured by indo-1) and twitch contractionssurrogate
A portion of calcium influx during depolarization in guinea-pig ventricular myocytes is rapidly buffered by the sarcoplasmic reticulum.
Cite This Study
Janczewski et al. (1993) studied this question.