Contribution of phosphodiesterase isozymes to the regulation of the L‐type calcium current in human cardiac myocytes
K Kajimoto, N Hagiwara, H Kasanuki… - British journal of …, 1997 - Wiley Online Library
K Kajimoto, N Hagiwara, H Kasanuki, S Hosoda
British journal of pharmacology, 1997•Wiley Online Library1 To determine the contribution of the various phosphodiesterase (PDE) isozymes to the
regulation of the L‐type calcium current (ICa (L)) in the human myocardium, we investigated
the effect of selective and non‐selective PDE inhibitors on ICa (L) in single human atrial
cells by use of the whole‐cell patch‐clamp method. We repeated some experiments in rabbit
atrial myocytes, to make a species comparison. 2 In human atrial cells, 100 μm pimobendan
increased ICa (L)(evoked by depolarization to+ 10 mV from a holding potential of− 40 mV) …
regulation of the L‐type calcium current (ICa (L)) in the human myocardium, we investigated
the effect of selective and non‐selective PDE inhibitors on ICa (L) in single human atrial
cells by use of the whole‐cell patch‐clamp method. We repeated some experiments in rabbit
atrial myocytes, to make a species comparison. 2 In human atrial cells, 100 μm pimobendan
increased ICa (L)(evoked by depolarization to+ 10 mV from a holding potential of− 40 mV) …
- 1To determine the contribution of the various phosphodiesterase (PDE) isozymes to the regulation of the L‐type calcium current (ICa(L)) in the human myocardium, we investigated the effect of selective and non‐selective PDE inhibitors on ICa(L) in single human atrial cells by use of the whole‐cell patch‐clamp method. We repeated some experiments in rabbit atrial myocytes, to make a species comparison.
- 2In human atrial cells, 100 μM pimobendan increased ICa(L) (evoked by depolarization to +10 mV from a holding potential of −40 mV) by 250.4±45.0% (n=15), with the concentration for half‐maximal stimulation (EC50) being 1.13 μM. ICa(L) was increased by 100 μM UD‐CG 212 by 174.5±30.2% (n=10) with an EC50 value of 1.78 μM in human atrial cells. These two agents inhibit PDE III selectively.
- 3A selective PDE IV inhibitor, rolipram (1–100 μM), did not itself affect ICa(L) in human atrial cells. However, 100 μM rolipram significantly enhanced the effect of 100 μM UD‐CG 212 on ICa(L) (increase with UD‐CG 212 alone, 167.9±33.9, n=5; increase with the two agents together, 270.0±52.2%; n=5, P<0.05). Rolipram also enhanced isoprenaline (5 nM)‐stimulated ICa(L) by 52.9±9.3% (n=5) in human atrial cells.
- 4In rabbit atrial cells, ICa(L) at +10 mV was increased by 22.1±9.0% by UD‐CG 212 (n=10) and by 67.4±12.0% (n=10) by pimobendan (each at 100 μM). These values were significantly lower than those obtained in human atrial cells (P<0.0001). Rolipram (1–100 μM) did not itself affect ICa(L) in rabbit atrial cells. However, ICa(L) was increased by 215.7±65.2% (n=10) by the combination of 100 μM UD‐CG 212 and 100 μM rolipram. This value was almost 10 times larger than that obtained for the effect of 100 μM UD‐CG 212 alone.
- 5These results imply a species difference: in the human atrium, the PDE III isoform seems dominant, whereas PDE IV may be more important in the rabbit atrium for regulating ICa(L). However, PDE IV might contribute significantly to the regulation of intracellular cyclic AMP in human myocardium when PDE III is already inhibited or when the myocardium is under β‐adrenoceptor‐mediated stimulation.
British Journal of Pharmacology (1997) 121, 1549–1556; doi:10.1038/sj.bjp.0701297
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