HCN4-GCaMP8 transgenic mice express the fluorescent calcium indicator GCaMP8 under control of the Hcn4 locus promoter/enhancer regions within the BAC transgene. HCN4-GCaMP8 transgenic mice from founder line B10-3 (R24:B10:L3) exhibit high sensor expression in heart (SA and AV nodes) and nervous system (brain and spinal cord). Specifically, expression is observed in the developing 13.5 dpc heart and in the brain and spinal cord. In total, transgene expression is consistent with endogenous Hcn4. In the absence of calcium binding, low/baseline EGFP fluorescence is observed. Following calcium binding (such as arteriolar vasodilation), bright EGFP fluorescence is observed at several-fold greater levels than baseline (see GCaMP8 details below). Hemizygous mice are viable and fertile with no reported gross physical or behavioral abnormalities. The donating investigator reports that breeding hemizygous mice together results in normal numbers of pups. To date (February 2016), it has not been specifically determined if the pups were hemizygous or homozygous genotype. Calcium is a key molecular signal for cell functions including heart, smooth muscle, vessel, and airway contraction, lung secretion, autonomic neurotransmission and immunocyte function. HCN4-GCaMP8 transgenic mice may be useful to examine calcium signaling in SA and AV nodes both in vivo and in vitro. The genetically encoded calcium indicator GCaMP8 is a sensitive GCaMP variant with high dynamic range and fast response kinetics (<a href="http://www.ncbi.nlm.nih.gov/pubmed/23240011">Ohkura et al. 2012 PLoS One 7:e51286</a>). Specifically, the high signal amplitude and low baseline fluorescence of GCaMP8 results in ability to detect single Ca2+ spikes / single neuronal action potentials. GCaMP8 has ~3-fold greater dynamic range than both GCaMP3 and GCaMP6, similar response kinetics to both GCaMP3 and GCaMP6, ~2-fold more rapid decay kinetics than GCaMP3 and lower baseline fluorescence than GCaMP3. In the absence of calcium binding, dim EGFP fluorescence is expected as there is a pore from the outside of its barrel into the chromophore. Upon calcium binding, this pore becomes occupied and bright EGFP fluorescence is observed at ~16-fold greater levels than baseline. In the presence of Ca2+, GCaMP8 has absorbance and emission peaks (~488 nm and ~510 nm, respectively). This mouse model is available by way of a collaborative effort between Cornell/National Heart Lung Blood Resource for Optogenetic Mouse Signaling (<a href="http://chromus.vet.cornell.edu">CHROMus</a>) and The Jackson Laboratory.


The fluorescent calcium indicator strain HCN4-GCaMP8 expresses GCaMP8 (a sensitive GCaMP variant with high dynamic range and fast response kinetics) in heart (SA and AV nodes) and nervous system (brain and spinal cord). Upon GCaMP8 binding to calcium, increased EGFP fluorescence is observed.

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