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Cardiovascular Research 1997 33(3):611-622; doi:10.1016/S0008-6363(96)00259-3
© 1997 by European Society of Cardiology
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Copyright © 1997, European Society of Cardiology

Restitution of contractility in single ventricular myocytes of guinea pig heart

Matti Vornanen1 and Neal Shepherd*

Research Service/15IL, Department of Veterans Affairs, Medical Center, 508 Fulton Street, Durham, NC 27705, USA

Objective: Our aim was to assess the extent to which changes in intracellular Ca2+ stores contribute to mechanical restitution in heart muscle. Methods: Single, isolated guinea pig ventricular cells were voltage clamped at –45 mV and stimulated continuously at 0.5 or 2 Hz with 200 ms depolarizing pulses (35 °C). The recoveries of the peak of contraction force (FP) and the calcium current (ICa) between beats were measured in contractions interpolated at various intervals (td) after a conditioning twitch. Recovery of SR Ca2+ load was inferred from the peak magnitude (Cpp) of similarly interpolated contractures, induced by rapid application of 5 mM caffeine. Results: For a conditioning stimulus rate of 0.5 Hz, both Fp and ICa were very small for small td and recovered along similar time courses with a t1/2 of about 50 ms. Cp was maximal at as early a time after a previous contraction as could be measured, at which time Fp was 56% of maximal. Cp declined throughout the stimulus interval to about 50% of its maximal value. Similar results were obtained for a conditioning stimulus rate of 2 Hz, at which rate both Fp and Cp were increased by a factor of 2. Conclusions: The time course of mechanical restitution is coincident with the recovery of ICa from inactivation. Caffeine-releasable intracellular calcium stores are fully recovered soon after a contraction and well before mechanical restitution is complete.

KEYWORDS Contractile function; Caffeine; Guinea pig, ventricular cells; Calcium, intracellular concentration; Calcium channel, L-type

1 Present address: Department of Biology, University of Joensuu, P.O. Box 111, 80101 Joensuu, Finland.

* Corresponding author. Tel. +1 919 286-0411, ext. 6502; Fax +1 919 286-6824.


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