Selectivity of felodipine for depolarized ventricular myocytes: a study at the single-cell level.
We studied the effects of felodipine (a second-generation dihydropyridine Ca2+ channel blocker) on excitation-contraction coupling (E-C coupling) in single isolated guinea-pig ventricular myocytes, using the whole-cell perforated patch-clamp technique or the Ca indicator, indo-1. Felodipine inhibited both L-type Ca2+ channel currents (ICa) and cell contractions in a concentration-dependent manner (10 pM to 100 nM) when we used a holding potential of -80 mV or -40 mV. The potency of felodipine was sharply dependent on a holding potential. Namely, use of a more depolarized holding potential markedly increased the potency of felodipine for inhibition of ICa and cell contraction. Next we current-clamped cells and obtained the resting membrane potential of -82 +/- 8 mV. When cells were current-injected at 0.1 Hz, exposure to 10 nM felodipine slightly but significantly diminished the amplitude of cell contractions (7.2 +/- 1.6 to 6.7 +/- 1.7 microns, P < 0.05) within 10 min. When cells were field stimulated, exposure of cells to 10 nM felodipine also slightly diminished the amplitude of cell shortening (5.1 +/- 2.0 to 4.6 +/- 1.9 microns, P < 0.05) and [Ca2+]i transients. We observed clear voltage-dependent blockade of E-C coupling by felodipine in ventricular myocytes. Thus, therapeutic concentrations (1-10 nM) of felodipine could inhibit E-C coupling in depolarized ventricular myocytes, which might simulate an ischemic or failing heart.
Kohmoto
O
O
Internal Medicine II, Faculty of Medicine, University of Tokyo, Japan. koumoto-2im@h.u-tokyo.ac.jp
Shimizu
T
T
Sugishita
K
K
Kinugawa
K
K
Takahashi
T
T
Serizawa
T
T
D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002465:Cell Movement / Q000187:drug effects; D048429:Cell Size / Q000187:drug effects; D004558:Electric Stimulation; D004594:Electrophysiology; D015736:Felodipine / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000166:cytology*; D018408:Patch-Clamp Techniques
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D015736:Felodipine