Calcium flux in turtle ventricular myocytes

Am J Physiol Regul Integr Comp Physiol. 2006 Dec;291(6):R1781-9. doi: 10.1152/ajpregu.00421.2006. Epub 2006 Aug 3.

Abstract

The relative contribution of the sarcoplasmic reticulum (SR), the L-type Ca(2+) channel and the Na(+)/Ca(2+) 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 Ca(2+) 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 Ca(2+) 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 Ca(2+) channels (I(Ca)). The density of I(Ca) was 3.2 +/- 0.5 pA/pF, which led to an overall total Ca(2+) influx of 64.1 +/- 9.3 microM/l. NCX activity was measured as the Ni(+)-sensitive current at two concentrations of intracellular Na(+) (7 and 14 mM). Total Ca(2+) influx through the NCX during depolarizing voltage steps to 0 mV was 58.5 +/- 7.7 micromol/l and 26.7 +/- 3.2 micromol/l at 14 and 7 mM intracellular Na(+), respectively. In the absence of the SR and L-type Ca(2+) 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 Ca(2+) used for contraction originates from the L-type Ca(2+) channel.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism*
  • Calcium Channels, L-Type / physiology*
  • Calcium Signaling / physiology*
  • Cells, Cultured
  • Heart Ventricles / cytology
  • Ion Channel Gating / physiology
  • Membrane Potentials / physiology
  • Myocytes, Cardiac / physiology*
  • Sarcoplasmic Reticulum / physiology*
  • Turtles / physiology*
  • Ventricular Function*

Substances

  • Calcium Channels, L-Type
  • Calcium