Ca2+-sensing Transgenic Mice

Genetically encoded signaling proteins provide remarkable opportunities to design and target the expression of molecules that can be used to report critical cellular events in vivo , thereby markedly extending the scope and physiological relevance of studies of cell function. Here we report the development of a transgenic mouse expressing such a reporter and its use to examine postsynaptic signaling in smooth muscle. The circularly permutated, Ca 2+ -sensing molecule G-CaMP (Nakai, J., Ohkura, M., and Imoto, K. (2001) Nat. Biotechnol . 19, 137-141) was expressed in vascular and non-vascular smooth muscle and functioned as a lineage-specific intracellular Ca 2+ reporter. Detrusor tissue from these mice was used to identify two separate types of postsynaptic Ca 2+ signals, mediated by distinct neurotransmitters. Intrinsic nerve stimulation evoked rapid, whole-cell Ca 2+ transients, or “Ca 2+ flashes,” and slowly propagating Ca 2+ waves. We show that Ca 2+ flashes occur through P2X receptor stimulation and ryanodine receptor-mediated Ca 2+ release, whereas Ca 2+ waves arise from muscarinic receptor stimulation and inositol trisphosphate-mediated Ca 2+ release. The distinct ionotropic and metabotropic postsynaptic Ca 2+ signals are related at the level of Ca 2+ release. Importantly, individual myocytes are capable of both postsynaptic responses, and a transition between Ca 2+ -induced Ca 2+ release and inositol trisphosphate waves occurs at higher synaptic inputs. Ca 2+ signaling mice should provide significant advantages in the study of processive biological signaling.