Angiotensin II inhibition of L-type Ca2+ current in sinoatrial node cells of rabbits

Abstract

The actions of angiotensin II (ANG II) were examined in the spontaneously active cells isolated from the rabbit sinoatrial node, using the nystatin-permeabilized, whole cell, patch-clamp method. At 30 nM, ANG II significantly lowered the spontaneous firing rate of the action potentials from 212 +/- 21 to 172 +/- 32 beats/min, with a concomitant reduction in the action potential amplitude. The voltage-clamp experiments showed that ANG II inhibited the L-type Ca2+ current (ICa) with a dissociation constant (Kd) of approximately 4 nM and a maximal inhibition of 30%. The inhibition was blocked by an AT1-receptor antagonist CV11974. Acetylcholine (ACh) at 10 microM reduced the ICa by 42 +/- 12%, and ANG II did not cause any further inhibition in the presence of ACh. At 100 nM, ANG II reduced the ICa by only 12% in the presence of 2 microM isoproterenol, and a similar inhibition was observed with 0.1 microM ACh. ANG II did not affect the dibutyryl adenosine 3',5'-cyclic monophosphate-stimulated ICa. Protein kinase C activator 12-O-tetra-decanoylphorbol-13-acetate did not mimic ANG II in the effects on ICa, and preincubation of the cells with calphostin C, a protein kinase C inhibitor, did not attenuate the ANG II effect. ANG II exerts a negative chronotropic effect in the pacemaker cells as its direct action through a pathway involving adenosine 3',5'-cyclic monophosphate-dependent protein kinase.

Intracellular Angiotensin II Regulates the Inward Calcium Current in Cardiac Myocytes

“…Moreover, the dialysis into the cell of PD 123,319 (10 Ϫ6 mmol/L), an angiotensin type 2 (AT 2 ) receptor blocking agent, performed in 6 myocytes did not alter the effect of the peptide on I Ca (nϭ6; PϾ0.05; not shown). Because there is evidence that Ang II when added to the bath reduces I Ca in cardiac pacemaker cells, 15 it is reasonable to think that the peptide dialyzed into the cytosol might leave the cell and interact with AT 1 receptors located at the surface cell membrane.…”

“…13 Previous observations by Allen et al 14 indicated that Ang II when added to the bath increases the L-type calcium current in cultured neonatal heart cells. Recently, Habuchi et al 15 demonstrated that in the sinoatrial node of the rabbit, Ang II reduces I Ca when added to the extracellular fluid.…”

Effects of Angiotensin II on the Action Potential Durations of Atrial Myocytes in Hypertensive Rats

“…In another study, Ang II induced spontaneous action potentials in partially depolarized preparations of rabbit atria and increased the rate of diastolic depolarization and spontaneous discharge in human atrial tissues (22). In rabbit sinoatrial node cells, Ang II depolarized the RMPs accompanied by a reduction of the action potential amplitude and a negative chronotropic effect (23). In isolated rabbit ventricular myocytes, Morita et al (24) reported that Ang II decreased the APD after 3 min of application, but prolonged the APD after application for 7 min.…”

Angiotensin II-induced inotropism requires an endocardial endothelium-nitric oxide mechanism in the in-vitro heart of Anguilla anguilla

“…In spontaneously beating heart preparations, ANG II induced negative chronotropism, which became significant at a concentration of 10 -9 ·mol·l -1 . Nanomolar concentrations of ANG II had a negative chronotropic effect in pacemaker cells of rabbit through modulation of the L-type Ca 2+ current (Habuchi et al, 1995). In electrically paced preparations, ANG II at 10 -8 ·mol · l -1 and 10 -7 ·mol·l -1 caused a significant decrease in VS and WS, indicating a direct negative modulation of mechanical performance.…”