Dihydropyridine-induced Ca2+ release from ryanodine-sensitive Ca2+ pools in human skeletal muscle cells.
Dihydropyridines (DHPs) are widely used antihypertensive drugs and inhibit excitation-contraction (E-C) coupling in vascular smooth muscle and in myocardial cells by antagonizing L-type Ca2+ channels (DHP receptors). However, contradictory reports exist about the interaction of the DHP with the skeletal muscle isoform of the DHP receptor and E-C coupling in skeletal muscle cells. Using the intracellular fluorescent Ca2+ indicator fura-2, an increase in [Ca2+]i was observed after extracellular application of nifedipine to cultured human skeletal muscle cells. The rise in [Ca2+]i was dose dependent with a calculated EC50 of 614 +/- 96 nM nifedipine and a maximum increment in [Ca2+]i of 80 +/- 3.2 nM. Similar values were obtained with nitrendipine. This effect of DHPs was restricted to differentiated skeletal muscle cells and was not seen in non-differentiated cells or in PC12 cells. In spite of the observed increase in [Ca2+]i, whole-cell patch clamp experiments revealed that 10 microM nifedipine abolished inward Ba2+ currents through L-type Ca2+ channels completely. Similar to nifedipine, (+/-)Bay K 8644, an agonist of the L-type Ca2+ channel, also increased [Ca2+]i. This effect could not be enhanced by further addition of nifedipine, suggesting that both DHPs act via a common signalling pathway. Based on the specific mechanism of the skeletal muscle E-C coupling, we propose the stabilization of a conformational state of the DHP receptor by DHPs, which is sufficient to activate the ryanodine receptor.
Weigl
L G
LG
Department of Anaesthesia and General Intensive Care Medicine, General Hospital Vienna, Wahringer Gurtel 18-20, A-1090 Vienna, Austria. lukas.weigl@univie.ac.at
Hohenegger
M
M
Kress
H G
HG
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002120:Calcium Channel Agonists / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D004095:Dihydropyridines / Q000494:pharmacology*; D006801:Humans; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009568:Nitrendipine / Q000494:pharmacology; D016716:PC12 Cells; D011487:Protein Conformation / Q000187:drug effects; D051381:Rats; D012433:Ryanodine / Q000494:pharmacology*; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism
D002120:Calcium Channel Agonists; D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D004095:Dihydropyridines; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009568:Nitrendipine; D009543:Nifedipine; D002118:Calcium