Fig. 2.

Interrelations between APs and cytosolic Ca²⁺ transients in syncytial aGPVM cultures; modulability by β-adrenergic stimulation. A: Baseline APs and Ca²⁺ transients in monolayer cultures without adrenergic stimulation. Aa: Exemplar isochrone maps for initial depolarization during steady stimulation at indicated frequencies, derived from optical mapping of di-4-ANEPPS fluorescence. CV, conduction velocity. CV was calculated along line trajectories, and averaged. Ab: AP morphology averaged across monolayer; same monolayer as in Aa. Ac: Ca²⁺ transient averaged across different monolayer, using Rhod-2. Ad: CV restitution curve, averaged from n = 11 monolayers. Error bars, SEM throughout. Ae: AP duration (APD₈₀) restitution curve, averaged from n = 16 monolayers. Af: Ca²⁺ transient duration (Ca₈₀, black) recovery curve, averaged from n = 7 monolayers. For reference, APD₈₀ replotted from panel Ae as a function of cycle length (gray). B: Effect of isoproterenol on AP properties. Ba: Left and middle, spontaneous APs in exemplar monolayer, before and after exposure to isoproterenol (iso). This demonstrates a chronotropic effect. Right, average chronotropic effect across n = 11 monolayers (*, p < 0.01). Initial rate normalized to unity. Bb: Corresponding shortening of AP duration upon β-adrenergic stimulation. Left, exemplar APs averaged across another monolayer, ± iso. Steady 3 Hz pacing. Right, AP restitution curve ± 0.5 μM isoproterenol, averaged across n = 11 monolayers. Significant AP shortening by iso (*, p < 0.01). C: Effect of isoproterenol on Ca²⁺ transients, during 3 Hz stimulation. Ca: Lack of inotropic effect. Left, Ca²⁺ waveforms ± iso, averaged across n = 8 preparations. Right, corresponding bar graph summary. Cb: Isoproterenol nonetheless speeds Ca²⁺ transient relaxation. Left, normalized relaxation phase of Ca²⁺ transients, averaged across n = 8 preparations. Bar-graph summary of time constants for single-exponential fits to relaxation phase of Ca²⁺ transients (*, p < 0.01).