Figure 4.

BM3h-based sensors measure dopamine release in cell culture. (a) PC12 cells depolarized by addition of 54 mM K⁺ were stimulated to release dopamine (DA) into supernatants containing a BM3h-based sensor; cells did not release dopamine after addition of 54 mM Na⁺. (b) T₁-weighted spin echo MRI signal amplitudes (TE/TR = 10/477 ms) measured from the supernatants of PC12 cells incubated with 32 μM BM3h-B7 in the presence of K⁺ (stimulus) or Na⁺ (control). Inset, MRI image of microtiter wells under corresponding conditions. (c) Relaxation rates measured from the samples in b, minus the relaxation rate of buffer not containing BM3h-based sensors. Given the approximate concentration of BM3h variants in these samples, the Δ(1/T₁) values presented here can be converted to apparent relaxivities of 0.23 and 0.50 mM⁻¹ s⁻¹ in K⁺ and Na⁺ incubation conditions, respectively. (d) Data from c were used to estimate the concentrations of dopamine present in samples treated with K⁺ and Na⁺ (dark bars). We independently measured the concentrations of dopamine under equivalent conditions using ELISA (light bars).