[Na +] in the subsarcolemmal ‘fuzzy’ space and modulation of [Ca 2+] i and contraction in cardiac myocytes

• Published in: Cell calcium (Edinburgh) Vol. 35; no. 6; pp. 603 - 612
• Main Authors: Verdonck, Fons, Mubagwa, Kanigula, Sipido, Karin R.
• Format: Journal Article
• Language: English
• Published: Elsevier India Pvt Ltd 01.06.2004
• Subjects: Cardiac myocytes; Excitation-contraction coupling; Na; T-tubules; ‘Fuzzy’ space; ‘Fuzzy’ space; Na; T-tubules; Excitation-contraction coupling; Cardiac myocytes
• ISSN: 0143-4160; 1532-1991
• DOI: 10.1016/j.ceca.2004.01.014

The strength of the heart beat depends on the amplitude and time course of the transient increase in [Ca 2+] in the myocytes with each cycle. [Na +] i modulates cardiac contraction through its effect on the Ca 2+ flux through the Na/Ca exchanger. Cardiac excitation–contraction coupling has been postulated to occur in a microdomain or ‘fuzzy’ space at the junction of the T-tubules and the sarcoplasmic reticulum. This ‘fuzzy’ space is well described for the Ca 2+ fluxes and the interaction between the L-type Ca 2+ channel, the Ca 2+ release channel of the sarcoplasmic reticulum and the Na/Ca exchanger. Co-localization of the Na + transporters, in particular the Na/K pump and the Na + channel, within this ‘fuzzy’ space is not as well established. The functional and morphological characteristics of the ‘fuzzy’ space for Na + and its interaction with the Ca 2+ handling suggest that this space is not strictly co-inciding with the Ca 2+ microdomain. In this space [Na +] can be several-fold higher or lower than [Na +] in the bulk cytosol. This has implications for modulation of [Ca 2+] i during a single beat as well as during alterations in Na + fluxes seen in pathological conditions.