Fig. 8.

Intracellular cAMP production depends on Ca²⁺_i transients. cAMP was measured in non-stimulated (a and c) and NA-stimulated (b and d) SAN cell samples, either pre-treated with vehicle (open symbols) or Ca²⁺_i transient inhibiting drugs (filled symbols). a, b cAMP–MCh relationship in the absence (vehicle) and presence of 3 μM ryanodine in non-stimulated (a) and NA-stimulated (b) cells. c, d cAmp–MCh relationship in the absence (vehicle) and presence of 25 μM BAPTA-AM in non-stimulated (c) and NA-stimulated (d) cells. All cAMP values were normalized to the control cAMP levels of non-stimulated SAN cells in the absence of ACh. Asterisks indicate significant difference between vehicle and Ca²⁺_i transient inhibiting drug at the associated MCh concentration