Insights into the pathogenesis of migraine with aura may be gained from a study of human Ca_V2.1 channels containing mutations linked to familial hemiplegic migraine (FHM). Here, we extend the previous single-channel analysis to human Ca_V2.1 channels containing mutation V1457L. This mutation increased the channel open probability by shifting its activation to more negative voltages and reduced both the unitary conductance and the density of functional channels in the membrane. To investigate the possibility of changes in Ca_V2.1 function common to all FHM mutations, we calculated the product of single-channel current and open probability as a measure of Ca²⁺ influx through single Ca_V2.1 channels. All five FHM mutants analyzed showed a single-channel Ca²⁺ influx larger than wild type in a broad voltage range around the threshold of activation. We also expressed the FHM mutants in cerebellar granule cells from Ca_V2.1α₁^−/− mice rather than HEK293 cells. The FHM mutations invariably led to a decrease of the maximal Ca_V2.1 current density in neurons. Current densities were similar to wild type at lower voltages because of the negatively shifted activation of FHM mutants. Our data show that mutational changes of functional channel densities can be different in different cell types, and they uncover two functional effects common to all FHM mutations analyzed: increase of single-channel Ca²⁺ influx and decrease of maximal Ca_V2.1 current density in neurons. We discuss the relevance of these findings for the pathogenesis of migraine with aura.