Abstract
Calmodulin (CaM) interactions with Ca$^2+$ channels mediate both
Ca$^2+$ regulation of channels and local Ca$^2+$ triggering
of transcription factors implicated in neuronal memory. Crucial to
these functions are the number of CaM molecules (CaMs) regulating
each channel, and the number of CaMs privy to the local Ca$^2+$
signal from each channel. To resolve these parameters, we fused L-type
Ca$^2+$ channels to single CaM molecules. These chimeric molecules
revealed that a single CaM directs L-type channel regulation. Similar
fusion molecules were used to estimate the local CaM concentration
near Ca$^2+$ channels. This estimate indicates marked enrichment
of local CaM, as if a "school" of nearby CaMs were poised to enhance
the transduction of local Ca$^2+$ entry into diverse signaling
pathways.
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