Compared to freshly isolated SANC (f-SANC), the spontaneous AP firing rate at 34±0.5oC of cultured adult rabbit SANC (c-SANC) is reduced by 50% (from 2.79Hz to 1.35Hz), due to Gi protein suppression of basal cAMP/PKA/Ca2+-dependent signaling. Here we demonstrate that altered PKA-dependent modulation of basal intracellular Ca2+ cycling also reduces AP rhythmicity of c-SANC.The AP rhythmicity index (RI, fig.1A), i.e. the offset of the 3rd peak from the autocorrelation function of AP records, or from power spectrum analysis is reduced in c- vs. f-SANC, and is associated with prolongation of spontaneous Local Ca2+ Releases (LCR) period during diastolic depolarization and an increase in its coefficient of variation (0.199 ± 0.014 (n=41) for c-SANC vs. 0.122 ± 0.009 (n=32) for f-SANC, p<0.001). Acute β-adrenergic receptor stimulation by isoproterenol (ISO), phosphodiesterase inhibition by 3-isobutyl-1-methylxanthine (IBMX), or prolonged Gi suppression by pertussis toxin (PTX), which rescues impaired cAMP/PKA signaling in c-SANC, not only rescues the reduced AP firing rate, but also restores normal variability of LCR period and restores the rhythmicity of AP firing to the f-SANC level (fig.1B).View Large Image | View Hi-Res Image | Download PowerPoint Slide