Declining into failure: the age-dependent loss of the L-type calcium channel within the sinoatrial node.
BACKGROUND
The spontaneous activity of pacemaker cells in the sinoatrial (SA) node controls heart rate under normal physiological conditions. Clinical studies have shown the incidence of SA node dysfunction increases with age and occurs with peak prevalence in the elderly population. The present study investigated whether aging affected the expression of Ca(v)1.2 channels and whether these changes could affect pacemaker activity, in turn leading to age-related SA node degeneration.


RESULTS
The SA node region was isolated from the right atrium of guinea pigs between birth and 38 months of age. Immunofluorescence studies showed Ca(v)1.2 protein was present as punctate labeling around the outer membrane of atrial cells but was absent from the center of the SA node. The area lacking Ca(v)1.2-labeled protein progressively increased from 2.06+/-0.1 (mean+/-SEM) mm2 at 1 month to 18.72+/-2.2 mm2 at 38 months (P<0.001). Western blot provided verification that Ca(v)1.2 protein expression within the SA node declined during aging. Functional measurements showed an increased sensitivity to the L-type calcium blocker nifedipine; SA node preparations stopped beating in 100 micromol/L nifedipine at 1 day old, compared with 30 micromol/L at 1 month and 10 micromol/L at 38 months of age. Furthermore, the amplitude of extracellular potentials declined within the center and periphery of the SA node during aging.


CONCLUSIONS
The present data show Ca(v)1.2 channel protein decreases concurrently with reduced spontaneous activity of the SA node with increased age, which provides further evidence of mechanisms underlying the age-related deterioration of the cardiac pacemaker.
Jones
Sandra A
SA
Institute of Membrane and Systems Biology, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom. s.a.jones@leeds.ac.uk
Boyett
Mark R
MR
Lancaster
Matthew K
MK
D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D004594:Electrophysiology; D006168:Guinea Pigs; D006339:Heart Rate / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D009924:Organ Culture Techniques; D012849:Sinoatrial Node / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D013995:Time
D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C); D009543:Nifedipine; D002118:Calcium