Molecular basis of the T‐ and L‐type Ca 2+ currents in canine Purkinje fibres

This study examines the molecular basis for the T‐type and L‐type Ca 2+ currents in canine Purkinje cells. The I CaT in Purkinje cells was completely suppressed by 200 n m 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 Ca 2+ channels in canine Purkinje cells. This conclusion is consistent with the sensitivity of the current to blockade by Ni 2+ ions ( K D = 32 μ 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.