Splice-variant-specific effects of primary aldosteronism point mutations on human Ca_V3.2 calcium channels

Ca_V3.2 calcium channels play important roles in both neural excitability and aldosterone secretion. Recent clinical studies found four germline mutations (S196 L, M1549I, V1951E and P2083 L) in Ca_V3.2 channels. All four mutations caused primary aldosteronism (PA), while only the M1549I mutation resulted in obvious neural malfunctions besides PA. In human, there are two major Ca_V3.2 channel gene (CACNA1H) splice variants, either with or without exon 26. In this study, we tested the expression of the two CACNA1H splice variants in zona glomerulosa (ZG) cells of human adrenal cortex and the possibility that Ca_V3.2 (-26) and Ca_V3.2 (+26) channels have different functional responses to the four PA mutations. We found that human ZG cells only express long form Ca_V3.2(+26) channels. The M1549I mutation slowed the inactivation of Ca_V3.2(+26) more than 5 fold, and Ca_V3.2(-26) more than 2 fold. The S196 L, V1951E and P2083 L mutations accelerated channel recovery from inactivation for Ca_V3.2(+26), but not Ca_V3.2(-26) channels. All four mutations resulted in gain of function of Ca_V3.2(+26) channels, leading to overproduction of aldosterone. In conclusion, the four PA mutations caused more profound changes on Ca_V3.2 (+26) currents than on Ca_V3.2 (-26) currents, and except the M1549I mutation, the S196 L, V1951E and P2083 L have little effect on the electrophysiological properties of Ca_V3.2(-26) currents, which may partially explain the limitation of the phenotype associated with the V1951E, S196 L and P2083 L germline mutations to PA.