title: Modulation of ICa-L by alpha1-adrenergic stimulation in rat ventricular myocytes.
abstract: We found when L-type calcium current (ICa-L) was recorded with the perforated patch-clamp method in rat ventricular myocytes that bath application of phenylephrine (with propranolol) evoked a biphasic response characterized by an initial transient suppression followed by a sustained potentiation. The transient suppression occurred 30-60 s after phenylephrine perfusion and reached peak inhibition at approximately 2 min. The biphasic modulation of ICa-L was also elicited by methoxamine, and the effects of phenylephrine were blocked by prazosin, indicating that the responses were mediated through alpha1-adrenoceptors. Pretreatment of cells with H7 (100 micromol/L), a broad-spectrum protein kinase inhibitor that inhibits both protein kinase C and A, eliminated potentiation but did not affect transient suppression. The transient suppression occurred concurrently with the acceleration of the fast component of ICa-L inactivation. Depletion of intracellular Ca2+ stores by ryanodine plus caffeine or thapsigargin eliminated the transient suppression. When ICa-L was recorded with whole-cell patch-clamp and with 0.05 mmol/L EGTA in the pipette solution to allow intracellular Ca2+ to fluctuate, phenylephrine evoked a transient suppression as in the perforated patch recordings. Heparin, a specific blocker of IP3 (inositol 1,4,5-trisphosphate) receptors, eliminated the phenylephrine-induced transient suppression of ICa-L when added to the pipette solution. Intensive chelation of intracellular Ca2+ by 5 mmol/L BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid) in the pipette solution also eliminated the phenylephrine-induced transient suppression of ICa-L. We conclude that transient increase in the concentration of intracellular calcium ([Ca2+]i) caused by Ca2+ release from intracellular stores underlies the transient suppression of ICa-L, whereas the potentiation of ICa-L is a result of activation of protein kinases.
authors.affiliation: Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre and Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, MB, Canada. szhang@sbrc.ca
authors.forename: Shetuan
authors.initials: S
authors.lastname: Zhang
authors.forename: Jijin
authors.initials: J
authors.lastname: Lin
authors.forename: Yuji
authors.initials: Y
authors.lastname: Hirano
authors.forename: Masayasu
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D015544:Inositol 1,4,5-Trisphosphate; D008729:Methoxamine / Q000494:pharmacology; D032342:Muscle Cells / Q000187:drug effects / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D051381:Rats; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism; D016276:Ventricular Function
chemical_list: D058646:Adrenergic alpha-1 Receptor Agonists; D058668:Adrenergic alpha-1 Receptor Antagonists; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D000319:Adrenergic beta-Antagonists; D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D018340:Receptors, Adrenergic, alpha-1; D010656:Phenylephrine; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D015544:Inositol 1,4,5-Trisphosphate; D011433:Propranolol; D011493:Protein Kinase C; D008729:Methoxamine; D002118:Calcium; D011224:Prazosin