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Protein kinase-C mediates dual modulation of L-type Ca2+ channels in human vascular smooth muscle
1Institut für Pharmakologie und Toxikologie, Universität Graz, Austria.
Abstract:
The role of protein kinase C (PKC) in cellular regulation of L-type Ca2+ channels was investigated in human umbilical vein smooth muscle. Activation of PKC, by low concentrations (< 30 nM) of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) caused inhibition of Ca2+ channels, while higher concentrations of TPA (> 100 nM) elicited a transient rise, followed by sustained inhibition of Ca2+ channel activity in cell-attached patches. Low TPA concentrations predominantly reduced channel availability, while high concentrations of TPA (100 nM) transiently increased channel availability and, in addition, prolonged mean open time. The inactive 4-alpha-phorbol-12,13- didecanoate failed to affect channel activity, and pretreatment of the cells with PKC inhibitors (H-7, chelerythrine) antagonized inhibitory and stimulatory effects of TPA. Our results provide evidence for two distinct PKC-dependent mechanisms of L-type Ca2+ channel regulation in smooth muscle.
Insights
Protein kinase C (PKC) differentially regulates L-type Ca2+ channels in smooth muscle. Low concentrations of TPA inhibit channels, while high concentrations cause transient potentiation followed by inhibition.
Area of Science:
- Physiology
- Molecular Biology
- Pharmacology
Background:
- Protein kinase C (PKC) plays a crucial role in cellular signaling pathways.
- L-type Ca2+ channels are critical for regulating cellular excitability and function, particularly in smooth muscle.
- Understanding PKC's modulation of these channels is key to comprehending smooth muscle physiology.
Purpose of the Study:
- To investigate the specific mechanisms by which protein kinase C (PKC) regulates L-type Ca2+ channels in human umbilical vein smooth muscle cells.
- To differentiate the effects of varying concentrations of a PKC activator, TPA, on channel activity.
Main Methods:
- Patch-clamp electrophysiology was used to record L-type Ca2+ channel activity in cell-attached patches.
- Activation of PKC was achieved using 12-O-tetradecanoyl-phorbol-13-acetate (TPA) at different concentrations.
- PKC inhibitors (H-7, chelerythrine) and an inactive phorbol ester were used to confirm PKC-dependent effects.
Main Results:
- Low TPA concentrations (< 30 nM) primarily inhibited L-type Ca2+ channel availability.
- High TPA concentrations (> 100 nM) initially increased channel availability and prolonged mean open time, followed by sustained inhibition.
- Effects of TPA were abolished by PKC inhibitors, confirming a PKC-dependent mechanism.
Conclusions:
- Two distinct PKC-dependent pathways modulate L-type Ca2+ channel activity in smooth muscle.
- PKC can exert both inhibitory and potentiating effects on these channels, depending on the concentration of the activator.
- These findings elucidate complex regulatory mechanisms of Ca2+ influx in smooth muscle.