J019 Functional consequences of inactivation of L-type cav1.3 and T-type Cav3.1 channels on in vivo pacemaker activity and calcium cycling in cardiac automatic cells

Cardiac automaticity, in normal conditions, is generated by the Sinoatrial Node (SAN) tissue. In the last years, two pacemaker mechanisms are proposed: the “ion channels clock”, based on the If current and the intracellular SR-dependent “Ca2+ clock”, based on spontaneous diastolic Ca2+ release. In our opinion a relevant role is played also by the Cav1.3 (L-type Ca2+ current) and Cav3.1 (T-type Ca2+ current) channels. For this reason we studied the two mouse models Cav1.3 KO and Cav1.3/Cav3.1 double KO in vivo and in vitro. Electrocardiograms analysis showed a strong bradycardia (p<0.01). Respectively the Heart Rate (HR) of Cav1.3 KO and Cav1.3/Cav3.1 double KO are: 396.3 ± 39.4 bpm (N.4) and 360.9 ± 53.1 bpm (N.3); instead in WT the HR is 545.4 ± 29.6 bpm (N.9). In addition we detected in the two mouse model a marked arrhythmia determined by the presence of many blocks of first and second degree. Particularly Cav1.3/Cav3.1 double KO showed a dissociation of rhythm. In vitro analysis was performed with the line scan technique on WT and Cav1.3 KO SAN cells to observe the dynamics of Ca2+ release. The results seem to indicate a difference in the frequency of transients that is reduced in Cav1.3 KO compared with WT. Moreover the transient length result to be longer in Cav1.3 KO 1248.9 ± 341.5 ms (N.8) than in WT 831.7 ± 259.7 ms (N.5). Interesting results are obtained also after the analysis of the differents parts of transient, as expected the recovery phase result longer in Cav1.3 KO 1053.5 ± 313.3 ms (N.5) than in WT 553.9 ± 178.5 ms (N.8), instead the ramp phase result longer in WT 192.5 ± 72.18 ms (N.8) than in Cav1.3 KO 83.25 ± 38 ms (N.5). In conclusion our date indicate that the absence of Cav1.3 channel cause the slowdown of pace maker mechanism at the in vivo and in vitro level. More experiments are needed to draw clears conclusions about the role of Cav3.1 channel, but seem to be important in cardiac automaticity generation.