Key result
Depolarization-triggered secretion was elevated to a similar extent by forskolin in chromaffin cells expressing either the wild-type or S1898A mutated human α(1)1.2 subunit.
The study suggests that additional PKA regulatory sites at the C-tail of the α(1)1.2 subunit are involved in regulating catecholamine secretion, as the S1898 site alone is not essential for forskolin-induced increases in secretion.
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Animal data leave open which PKA sites on α(1)1.2 regulate catecholamine secretion; no clinical implications yet.
A PKA consensus phosphorylation site S1928 at the α(1)1.2 subunit of the rabbit cardiac L-type channel, Ca(V)1.2, is involved in the regulation of Ca(V)1.2 kinetics and affects catecholamine secretion. This mutation does not alter basal Ca(V)1.2 current properties or regulation of Ca(V)1.2 current by PKA and the beta-adrenergic receptor, but abolishes Ca(V)1.2 phosphorylation by PKA. Here, we test the contribution of the corresponding PKA phosphorylation site of the human α(1)1.2 subunit S1898, to the regulation of catecholamine secretion in bovine chromaffin cells. Chromaffin cells were infected with a Semliki-Forest viral vector containing either the human wt or a mutated S1898A α(1)1.2 subunit. Both subunits harbor a T1036Y mutation conferring nifedipine insensitivity. Secretion evoked by depolarization in the presence of nifedipine was monitored by amperometry. Depolarization-triggered secretion in cells infected with either the wt α(1)1.2 or α(1)1.2/S1898A mutated subunit was elevated to a similar extent by forskolin. Forskolin, known to directly activate adenylyl-cyclase, increased the rate of secretion in a manner that is largely independent of the presence of S1898. Our results are consistent with the involvement of additional PKA regulatory site(s) at the C-tail of α(1)1.2, the pore forming subunit of Ca(V)1.2.
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Bachnoff et al. (2011) studied this question. Mutated S1898A α(1)1.2 subunit vs. Wild-type α(1)1.2 subunit was evaluated on Depolarization-triggered secretion in the presence of nifedipine and forskolin. Depolarization-triggered secretion was elevated to a similar extent by forskolin in chromaffin cells expressing either the wild-type or S1898A mutated human α(1)1.2 subunit.
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