Fig. 4
Control of basal I Ca,L by β-AR-PKA signaling cascade in HAMs. a The myocyte was exposed to ACh (10 µM) alone and again after stimulation of I Ca,L with ISO (1 µM). The dotted line indicates spontaneous run-down. The current traces shown in the inset were recorded at the times indicated by the corresponding letters on the main graphs. b After stimulation of I Ca,L with ISO (1 µM), the intracellular solution was changed to one containing 20 µM PKI(15-22), and the current was inhibited below the control level. c H-89 (10 µM), a cell permeant inhibitor of PKA, inhibited basal I Ca,L and prevented its stimulation by ISO (1 µM). d IBMX (100 µM) near maximally stimulated basal ICa,L. e The myocyte was superfused with Cal A (100 nM) and when the current amplitude reached a steady-state, ISO (1 µM) induced additional stimulation of I Ca,L. f Propranolol (1 µM), an inverse agonist of β-ARs, inhibited basal I Ca,L. g Bar graphs summarizing the effects of all compounds tested in a–f on I Ca,L. *p < 0.05, **p < 0.01, ***p < 0.005, compared with basal I Ca,L