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Updated: Aug 11, 2026
Primary Culture of Adult Rat Heart Myocytes
Published on: June 16, 2009
Modulation of ICa-L by alpha1-adrenergic stimulation in rat ventricular myocytes
Shetuan Zhang1, Jijin Lin, Yuji Hirano
1Institute 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
Insights
Phenylephrine causes a temporary decrease in L-type calcium current (ICa-L) in rat heart cells, followed by a lasting increase. This biphasic response involves intracellular calcium release and protein kinase activation via alpha1-adrenoceptors.
Area of Science:
- Cardiovascular Physiology
- Molecular Pharmacology
- Cellular Electrophysiology
Background:
- L-type calcium current (ICa-L) is crucial for cardiac contractility.
- Alpha-adrenergic receptor stimulation influences cardiac function.
- Mechanisms modulating ICa-L in ventricular myocytes require elucidation.
Purpose of the Study:
- To investigate the biphasic effects of phenylephrine on ICa-L in rat ventricular myocytes.
- To determine the signaling pathways involved in phenylephrine-induced ICa-L modulation.
Main Methods:
- Perforated and whole-cell patch-clamp electrophysiology in rat ventricular myocytes.
- Pharmacological agents: phenylephrine, methoxamine, propranolol, prazosin, H7, ryanodine, caffeine, thapsigargin, heparin, BAPTA.
- Manipulation of intracellular calcium ([Ca2+]i) stores and signaling pathways.
Main Results:
- Phenylephrine induced a transient suppression and sustained potentiation of ICa-L.
- The transient suppression was mediated by alpha1-adrenoceptors and involved intracellular calcium release via IP3 receptors.
- The potentiation was mediated by protein kinase activation (PKC/PKA), as indicated by H7 inhibition.
Conclusions:
- Transient suppression of ICa-L is caused by a rapid increase in intracellular calcium from intracellular stores.
- Sustained potentiation of ICa-L results from protein kinase activation.
- Alpha1-adrenoceptor stimulation elicits complex, biphasic modulation of cardiac ICa-L through distinct signaling pathways.
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.
