Proceedings of The Physiological Society
Kings College London (2005) J Physiol 565P, C181
Are T-type calcium channels causally involved in neonatal cardiac myocyte hypertrophy?
McLatchie, Linda ; Butt, Busma ; Brooks, Gavin ; Shattock, Michael ;
1. Rayne Institute, King's college London, London, United Kingdom. 2. Cardiovascular Research Group, University of Reading, Reading, United Kingdom.
Cardiac myocyte hypertrophy although initially a compensative mechanism seen in response to stresses such as hypertension or myocardial infarction often becomes a major cardiovascular risk factor leading to congestive heart failure and death. T-type calcium channels have been associated with cardiac hypertrophy (Nuss & Houser, 1993) but it is unclear whether they play a direct causal role. This study aims to address this question. Neonatal rats (P1-P2) were killed by cervical dislocation and cardiac myocytes isolated by enzymatic digestion. Myocytes were cultured without electrical stimulation for 96 hours to allow 24 hours recovery, 48 hours quiescence in 0% serum then 24 hours with either 20% serum to induce hypertrophy or 0% serum control (Vara et al. 2003). Cell size, measured as cell area under the microscope, increased significantly (p<0.05, t test) from 739 ± 48 μm2 (mean ± sem, n=288 cells from 8 preparations) in control cells maintained in 0% serum to 1579 ± 51 μm2 (mean ± sem, n=288 cells from 8 preparations) with 20% serum, a 2.2-fold increase indicating that the cells had undergone hypertrophy. Both groups were then treated with 3 different calcium channel blockers, Mibefradil, TTL1177 (formally TH-1177, Haverstick et al. 2000) and verapamil. These compounds all caused a significant (p<0.05 for all groups ANOVA) dose-dependent reduction in the induced hypertrophy as measured by cell size with IC50 values of 5.8 ± 1.3 μM) for Mibefradil, 5.0 ± 2.3 μM) for TTL1177 and 14.0 ± 2.3 μM for Verapamil (all values are means ± s.e.m, n=3 preparations; 36 cells at each of 4-6 concentrations for each preparation). These values are consistent with those known to block the CaV3.1 and CaV3.2 isoforms of T-type calcium channels shown by PCR to be present in these cells. Hypertrophy was not inhibited by verapamil at concentrations sufficient to block almost all L-type calcium channels and the value given here is consistent with T-type rather than L-type calcium channel block. Similar dose-dependent reduction in the hypertrophy-induced increase in cell size was also seen with these calcium channel blockers when hypertrophy was induced by either 100 nM phenylephrine or 10 nM endothelin-1. These data suggest that blocking T-type calcium channels is sufficient to inhibit the induction of hypertrophy seen in neonatal myocytes on application of hypertrophic stimuli and suggest that T-type calcium channels could play a direct causal role in cardiac hypertrophy.
Where applicable, experiments conform with Society ethical requirements