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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 Ca(v)3.1, whereas Ca(v)3.2 is present at moderate levels. The dominant HVA calcium channel transcript is Ca(v)1.2; only traces of Ca(v)1.3 mRNA are detectable in SA myocytes of mice.
Bohn et al. (Wed,) studied this question.