At the cellular level, cardiac pacemaking which sets the rate and rhythm of the heartbeat is produced by the slow diastolic depolarization. Several ion channels contribute to this pacemaker depolarization, including T-type and L-type calcium currents. To evaluate the molecular basis of the currents involved, we investigated the cellular distribution of various low voltage activated (LVA) and high voltage activated (HVA) calcium channel mRNAs in the murine sinoatrial (SA) node by in-situ hybridization. The most prominently expressed LVA calcium channel in the SA node is Cav3.1, whereas Cav3.2 is present at moderate levels. The dominant HVA calcium channel transcript is Cav1.2; only traces of Cav1.3 mRNA are detectable in SA myocytes of mice.
