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 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 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 
microM). 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.