Molecular basis of the T- and L-type Ca2+ currents in canine Purkinje fibres

This study examines the molecular basis for the T-type and L-type Ca2+ currents in canine Purkinje cells. The I-CaT in Purkinje cells was completely suppressed by 200 nM kurtoxin, a specific blocker of both Ca(v)3.1 and Ca(v)3.2 channels. Since only Ca(v)3.2 mRNA is expressed at high levels in Purkinje fibres, being approximately 100-fold more abundant than either Ca(v)3.1 or Ca(v)3.3 mRNAs, it is concluded that the Ca(v)3.2 gene encodes the bulk of the T-type Ca2+ channels in canine Purkinje cells. This conclusion is consistent with the sensitivity of the current to blockade by Ni2+ ions (K-D = 32 mu M). For L-type channels, Ca(v)1.2 mRNA was most abundant in Purkinje fibres but a significant level of Ca(v)1.3 mRNA expression was also found. A comparison of the sensitivity to blockade by isradipine of the L-type currents in Purkinje cells and ventricular epicardial myocytes, which only express Ca(v)1.2, suggests that the Ca(v)1.3 channels make, at most, a minor contribution to the L-type current in canine Purkinje cells.