The role of cytoplasmic calcium in the regulation of the resting potential in the pulmonary veins myocardium in rats and mice

We have demonstrated the phenomenon of Са²⁺-induced hyperpolarization in the myocardium of pulmonary veins (PVs) in rats. An increase in cytoplasmic calcium Са²⁺]_i was shown to shift the resting potential (RP) in the PVs towards more negative values. The compounds inducing an increase in Са²⁺]_i, such as isoproterenol (10 μM), caffeine (5 mM), and ryanodine (0.01 μM), caused hyperpolarization of 10 ± 2, 9 ± 1.3, and 4.1 ± 2 mV, respectively. The inhibition of calcium-dependent potassium currents (IK_Ca) did not change RP of PVs under the control conditions and did not affect the Са²⁺-induced hyperpolarization.