[Ca2+]i following extrasystoles in guinea-pig trabeculae microinjected with fluo-3 - a comparison with frog skeletal muscle fibres.

Abstract

Force production of cardiac muscle is highly dependent on the interval between the excitations. The aim was to investigate relations between intracellular calcium ([Ca2+]i) and force when a stimulus protocol, with three extrasystoles (ESs) at various intervals, was used. The relation between [Ca2+]i and force was compared with that in frog skeletal muscle fibre. Fluo-3 was microinjected into thin cardiac trabeculae to monitor [Ca2+]i. During steady-state [Ca2+]i consisted of a rapid rise (phase 1) that lasted until peak dF/dt (rate of force development) and was followed by a slower rise (phase 2) that coincided with the action potential and had a peak after peak force. The decline in [Ca2+]i outlasted the duration of the contraction. As the ES intervals were prolonged, there was a gradual restitution of force and of the amplitude and rate of rise of phase 1 [Ca2+]i. Peak dF/dt was linearly related to the amplitude of phase 1 [Ca2+]i during restitution and potentiation of force. Skeletal muscle fibres were loaded with fluo-3-AM. From [Ca2+]i the amount of calcium bound to troponin ([Ca-T]) as a function of time was estimated. Force production of the skeletal muscle fibre could be predicted from [Ca-T] when the signal was delayed (time constant 36 ms). This finding indicates that the recorded [Ca2+]i in skeletal muscle represents activator calcium. In cardiac muscle probably only phase 1 [Ca2+]i represents activator calcium. Phase 2 [Ca2+]i probably represents calcium entry during the action potential and does not activate the contractile system to any significant extent.

• Authors: B Wohlfart
• Journal: Acta physiologica Scandinavica (Acta Physiol Scand) Vol. 169 Issue 1 Pg. 1-11 (May 2000) ISSN: 0001-6772 [Print] England
• PMID: 10759605 (Publication Type: Comparative Study, Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Aniline Compounds
• Fluorescent Dyes
• Troponin
• Xanthenes
• Fluo-3
• Calcium

Topics

• Action Potentials (physiology)
• Aniline Compounds
• Animals
• Calcium (metabolism)
• Calibration
• Electric Stimulation
• Fluorescent Dyes
• Guinea Pigs
• Microinjections
• Muscle Contraction (physiology)
• Muscle Fibers, Skeletal (physiology)
• Muscle, Skeletal (cytology, metabolism)
• Myocardium (cytology, metabolism)
• Rana temporaria
• Species Specificity
• Systole (physiology)
• Troponin (metabolism)
• Xanthenes