Figure 4.

PKA changes the relationship between Ca²⁺ and transmitter release. The ability of forskolin (20 μM) to facilitate action potential-evoked IPSCs was evaluated at different concentrations of Ca²⁺ in control (A) and BontA-treated synapses (B). Forskolin caused the largest degree of facilitation at 2 and 6 mM Ca²⁺ in control and BontA treated synapses, respectively (Left). (Data are expressed as mean ± SEM. ∗, P < 0.05; n = 3–9). A Ca²⁺ to release relationship in the presence of forskolin was reconstructed by multiplying the relative IPSC amplitude of control cultures by the degree of forskolin-induced facilitation (Center) (Right, the same data on a log–log format). The data demonstrate that forskolin-dependent facilitation is accompanied by an increase in the slope of this relationship. Although BontA shifts the Ca²⁺ to release relationship to the right, it does not affect the ability of forskolin to increase the slope of the log–log plot of the Ca²⁺ to release relationship.