Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, C002

Oral Communications

Postnatal development of t-tubules and alterations in triggered calcium release in the sheep atria

C. Smith1, D. Eisner1, A. Trafford1, K. Dibb1

1. University of Manchester, Manchester, United Kingdom.

Transverse (t)-tubules are invaginations in the membranes of cardiac myocytes that facilitate synchronous calcium release and thus contraction. In diseases such as heart failure, atrial t-tubules are lost which contributes to reduced triggered calcium release and contractile dysfunction. Because of this the restoration of t-tubules is therapeutically desirable; however the process of t-tubule formation is not fully understood. T-tubules are absent at birth in the ventricles of small mammals, where they develop postnatally with subsequent changes in calcium handling. Nothing is currently known about the development of t-tubules and changes in calcium release in the atria. 1 week, 1 month, 3 months and adult sheep (~18 months) were euthanased with 200 mg/kg intravenous pentobarbitone and cells isolated from the left atrial appendage. T-tubule density was assessed using di-4-ANEPPS and confocal microscopy. Perforated patch clamp experiments were performed in Fluo-3 loaded cells to assess spatial calcium release. Data is presented as mean ± SEM, for n animals per group, compared by SPSS linear mixed models or two way repeated measures ANOVA where appropriate. T-tubule density increased during development with the fractional area of t-tubules increasing from 0.022±0.004 at 1 week, 0.045±0.004 at 1 month to 0.087±0.004 at 3 months where density was unchanged vs adult (0.067±0.01, p<0.001, n=6-11). As t-tubule density increased postnatally, there were improvements in the uniformity of calcium release throughout the cell. Whilst calcium transient amplitude was reduced in the cell centre compared to the surface by 24.0±10.9% in 1 week animals, this discrepancy was reduced to 15.4±11.4% at 1 month with no surface vs centre differences observed in 3 months and adult (p<0.01, n=7-10). When compared to the ventricle, triggered calcium release in the atria is patchy and occurs in discrete locations on the cell surface and in the cell centre - likely on t-tubules. In neonates where t-tubule density is less, the amplitude of calcium release at these discrete surface sites was 47.2±25.4% greater than release sites in the centre (p<0.001, n=8). T-tubules are present at birth in the sheep atria and develop until ~3 months of age where there is no further t-tubule development. Our data suggests that reduced t-tubule density results in reduced central calcium release in neonates that is compensated for by enhanced surface activity. In later life the synchronicity of calcium release throughout the cell is improved, coinciding with t-tubule maturation.

Where applicable, experiments conform with Society ethical requirements