Developmental Changes in the β-Adrenergic Modulation of Calcium Currents in Rabbit Ventricular Cells

• Published in: Circulation research Vol. 70; no. 1; pp. 104 - 115
• Main Authors: Osaka, Toshiyuki, Joyner, Ronald W
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD American Heart Association, Inc 01.01.1992; Lippincott
• Subjects: Action Potentials; Age Factors; Animals; Animals, Newborn; Biological and medical sciences; Calcium - physiology; Colforsin - administration & dosage; Colforsin - pharmacology; Cyclic AMP - physiology; Dose-Response Relationship, Drug; Female; Fundamental and applied biological sciences. Psychology; Heart; Heart Ventricles - cytology; Heart Ventricles - drug effects; In Vitro Techniques; Isoproterenol - pharmacology; Male; Rabbits; Ventricular Function; Vertebrates: cardiovascular system; Virulence Factors, Bordetella - pharmacology; Heart; Calcium; Nervous control; Enzyme; Cyclic AMP; Electrophysiology; Rabbit; Ions; Ionic current; Lagomorpha; Myocyte; β-Adrenergic receptor; Adenylate cyclase; Signal transduction; Vertebrata; Mammalia; Forskolin; Circulatory system; Inward current; Age; Biological receptor
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.res.70.1.104

We studied the developmental changes in the β-adrenergic modulation of L-type calcium current (ICa) in enzymatically isolated adult (AD) and newborn (NB, 1–4-day-old) rabbit ventricular cells using the whole-cell patch-clamp method. ICa was measured as the peak inward current at a test potential of +15 mV by applying a 180–450-msec pulse from a holding potential of −40 mV with Cs-rich pipettes and a K-free bath solution at room temperature. In control, ICa density (obtained by normalizing ICa to the cell capacitance) was significantly higher in AD cells (5.5±0.2 [mean±SEM] pA/pF, n=65) than in NB cells (2.6±0.1 pA/pF, n=60). Isoproterenol (ISO, 1 nM-30 μM) increased ICa in a dose-dependent manner for both groups. The maximal effect (Emax) of ISO, expressed as percent increase in ICa over control levels, and the concentration for one half of the maximal effect (EC50) were 203% and 51 nM, respectively, for AD cells and 111% and 81 nM, respectively, for NB cells. The effect of ISO (1 μM) on ICa was decreased as the test potential was increased from −10 to +40 mV. However, the ratio of the percent increase in ICa for AD versus NB cells was almost constant (2.09–2.45) at each test potential. Dose-response curves of forskolin (FOR, 0.3–50 μM) gave Emax and EC50 of 268% and 0.74 μM, respectively, for AD cells and 380% and 1.15 μM, respectively, for NB cells. After stimulating ICa by 10 μM ISO, the addition of 10 μM FOR produced a further increase in ICa of only 12±2% in AD cells (n=4) but a further increase of 140±41% in NB cells (n=6). FOR (10 μM) did not produce any increase in ICa for AD and NB cells after stimulating ICa by intracellular application of 200 μM cAMP. ICa density stimulated by 10 μM ISO (17.8±1.1 pA/pF, n=7), 10 μM FOR (21.0±1.3 pA/pF, n=8), or 200 μM cAMP (18.0±1.3 pA/pF, n=5) was equivalent in AD cells, whereas ICa density stimulated by 10 μM ISO (5.8±0.6 pA/pF, n=9) was significantly lower than that stimulated by either 10 μM FOR (13.8±1.5 pA/pF, n=7) or 200 μM cAMP (13.4±0.7 pA/pF, n=7) in NB cells. The ICa density for FOR or cAMP was significantly higher for AD than NB cells. Pretreatment of AD and NB cells with pertussis toxin markedly increased the ISO effect on ICa for NB cells, whereas the enhancement was relatively small for AD cells. We conclude that the effect of ISO to stimulate L-type ICa increases after birth in rabbit ventricular cells probably as a consequence of the reduction of tonic Gi inhibition of adenylate cyclase rather than the postnatal maturation of the β-receptor-adenylate cyclase system.