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A potential site of functional modulation by protein kinase A in the cardiac Ca2+ channel alpha 1C subunit
T Perets1, Y Blumenstein, E Shistik
1Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Ramat Aviv, Israel.
Abstract:
The well-characterized enhancement of the cardiac Ca2+ L-type current by protein kinase A (PKA) is not observed when the corresponding channel is expressed in Xenopus oocytes, possibly because it is fully phosphorylated in the basal state. However, the activity of the expressed channel is reduced by PKA inhibitors. Using this paradigm as an assay to search for PKA sites relevant to channel modulation, we have found that mutation of serine 1928 of the alpha 1C subunit to alanine abolishes the modulation of the expressed channel by PKA inhibitors. This effect was independent of the presence of the beta subunit. Phosphorylation of serine 1928 of alpha 1C may mediate the modulatory effect of PKA on the cardiac voltage-dependent ca2+ channel.
Insights
Protein kinase A (PKA) enhances cardiac calcium channels, but this effect is lost in oocytes. Mutation of serine 1928 in the alpha 1C subunit prevents PKA inhibitor effects, suggesting its role in channel modulation.
Area of Science:
- Cardiovascular Physiology
- Molecular Biology
- Ion Channel Function
Background:
- Protein kinase A (PKA) typically enhances cardiac Ca2+ L-type current.
- This enhancement is absent when the channel is expressed in Xenopus oocytes, potentially due to basal hyperphosphorylation.
- PKA inhibitors paradoxically reduce the activity of the expressed channel.
Purpose of the Study:
- To identify specific sites on the alpha 1C subunit involved in PKA-mediated modulation of cardiac Ca2+ channels.
- To utilize the observed PKA inhibitor effect in oocytes as an assay for functional site identification.
Main Methods:
- Site-directed mutagenesis of the alpha 1C subunit of the cardiac Ca2+ channel.
- Expression of wild-type and mutant channels in Xenopus oocytes.
- Assessing channel activity modulation by PKA inhibitors.
Main Results:
- Mutation of serine 1928 to alanine (S1928A) on the alpha 1C subunit abolished the inhibitory effect of PKA inhibitors on channel activity.
- This finding was independent of the presence of the beta subunit.
- The S1928A mutation specifically disrupted the PKA inhibitor-induced modulation.
Conclusions:
- Serine 1928 on the alpha 1C subunit is a critical site for PKA-mediated modulation of cardiac voltage-dependent Ca2+ channels.
- Phosphorylation of serine 1928 likely mediates the modulatory effects of PKA on cardiac Ca2+ channel function.
- This identifies a specific molecular mechanism underlying PKA regulation of cardiac ion channels.