Calcium flux in turtle ventricular myocytes

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    Abstract

    The relative contribution of the sarcoplasmic reticulum (SR), the L-type Ca2+ channel and the Na+/Ca2+ exchanger (NCX) were assessed in turtle ventricular myocytes using epifluorescent microscopy and electrophysiology. Confocal microscopy images of turtle myocytes revealed spindle-shaped cells, which lacked T-tubules and had a large surface area-to-volume ratio. Myocytes loaded with the fluorescent Ca 2+-sensitive dye Fura-2 elicited Ca2+ transients, which were insensitive to ryanodine and thapsigargin, indicating the SR plays a small role in the regulation of contraction and relaxation in the turtle ventricle. Sarcolemmal Ca2+ currents were measured using the perforated-patch voltage-clamp technique. Depolarizing voltage steps to 0 mV elicited an inward current that could be blocked by nifedipine, indicating the presence of Ca 2+ currents originating from L-type Ca2+ channels (I Ca). The density of ICa was 3.2 ± 0.5 pA/pF, which led to an overall total Ca2+ influx of 64.1 ± 9.3 μM/l. NCX activity was measured as the Ni+-sensitive current at two concentrations of intracellular Na+ (7 and 14 mM). Total Ca2+ influx through the NCX during depolarizing voltage steps to 0 mV was 58.5 ± 7.7 μmol/l and 26.7 ± 3.2 μmol/l at 14 and 7 mM intracellular Na +, respectively. In the absence of the SR and L-type Ca2+ channels, the NCX is able to support myocyte contraction independently. Our results indicate turtle ventricular myocytes are primed for sarcolemmal Ca 2+ transport, and most of the Ca2+ used for contraction originates from the L-type Ca2+ channel. Copyright © 2006 the American Physiological Society.
    Original languageEnglish
    Pages (from-to)R1781-R1789
    JournalAJP: Regulatory, Integrative and Comparative Physiology
    Volume291
    Issue number6
    DOIs
    Publication statusPublished - 2006

    Keywords

    • Excitation-contraction coupling
    • L-type Ca2+ channel
    • Na +/Ca2+ exchanger
    • Reptile
    • Sarcoplasmic reticulum

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