Smooth muscle protein kinase C

Protein kinase C (PKC) was first implicated in the regulation of smooth muscle contraction with the observation that phorbol esters induce slowly developing, sustained contractions. In some vascular smooth muscles, e.g., ferret aorta, phorbol ester induced contractions occur without an increase in sarcoplasmic free-Ca2+ concentration ([Ca]i) or myosin light chain phosphorylation. This response appears to be mediated by a Ca2+-independent isoenzyme of PKC (probably PKCε), since saponin-permeabilized single ferret aortic smooth muscle cells, which retain receptor coupling, developed force in response to phenylephrine at low free [Ca2+] (pCa 7.0–8.6) and the constitutively active proteolytic fragment of PKC (PKM) elicited a contraction at pCa 7 comparable with the phenylephrine-induced contraction. Both contractions were reversed by a pseudo-substrate peptide inhibitor of PKC. These observations suggest a mechanism whereby α-adrenergic agonists may elicit a contractile response without a Ca2+ signal: α-adrenergic stimulation of phosphatidylcholine-specific phosphoiipase C or D (the latter in conjunction with phosphatidate phosphohydrolase) generates diacylglycerol. In the absence of an increase in [Ca2+]i, diacylglycerol specifically activates so-called novel PKCs, of which ε is the only isoenzyme known to be expressed in vascular smooth muscle. Recent evidence suggests that PKC may trigger a cascade of phosphorylation reactions, resulting in activation of mitogen-activated protein kinase and phosphorylation of the thin filament associated protein caldesmon. Alternatively, or additionally, PKC may directly phosphorylate calponin, another thin filament associated protein. These phosphorylations are predicted to alleviate inhibition of the cross-bridge cycling rate by these thin-filament proteins. The slow development of force would then result from a slow rate of cross-bridge cycling due to the low basal level of myosin phosphorylation.Key words: protein kinase C, smooth muscle, calcium, caldesmon, calponin.

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Regulation of 4-aminopyridine-sensitive, delayed rectifier K+ channels in vascular smooth muscle by phosphorylation

Biochemistry and Cell Biology ◽

10.1139/o96-048 ◽

1996 ◽

Vol 74 (4) ◽

pp. 439-447 ◽

Cited By ~ 73

Author(s):

W. C. Cole ◽

O. Clément-Chomienne ◽

E. A. Aiello

Keyword(s):

Smooth Muscle ◽

Protein Kinase C ◽

Membrane Potential ◽

Protein Kinase ◽

Vascular Smooth Muscle ◽

Smooth Muscle Cells ◽

Muscle Protein ◽

Muscle Cells ◽

Delayed Rectifier ◽

Kinase C

Voltage-gated, delayed rectifier K+ current (KV) that is sensitive to 4-aminopyridine (4AP) block has been identified in all vascular smooth muscle tissues studied to date. These channels conduct outward, hyperpolarizing K+ current that influences resting membrane potential and contributes to repolarization of action potentials. Smooth muscle cells in most arterial resistance vessels regulate Ca2+ influx and contractile tone by low amplitude, tonic changes in membrane potential. Block of KV with 4-aminopyridine leads to contraction and an enhanced myogenic response to increased intravascular pressure. We investigated the modulation of KV currents in isolated, freshly dispersed smooth muscle cells from rabbit portal vein and coronary arteries in whole-cell voltage clamp experiments. Our findings indicate that KV channels are regulated by signal transduction mechanisms involving vasoactive agonists that activate cAMP-dependent protein kinase (PKA) or protein kinase C (PKC). In this paper, the properties and potential function of KV channels in vascular smooth muscle are reviewed. Further, the regulation and potential role of alterations in KV due to β-adrenoceptor agonists, adenylyl cyclase and PKA, as well as angiotensin II, diacylglycerol, and PKC are discussed.Key words: potassium channels, smooth muscle, protein kinase A, protein kinase C, membrane potential.

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Protein kinase C mediation of Ca2+-independent contractions of vascular smooth muscle

Biochemistry and Cell Biology ◽

10.1139/o96-053 ◽

1996 ◽

Vol 74 (4) ◽

pp. 485-502 ◽

Cited By ~ 116

Author(s):

Michael P. Walsh ◽

Odile Clément-Chomienne ◽

Jacquelyn E. Andrea ◽

Bruce G. Allen ◽

Arie Horowitz ◽

...

Keyword(s):

Signal Transduction ◽

Smooth Muscle ◽

Protein Kinase C ◽

Protein Kinase ◽

Light Chain ◽

Phorbol Esters ◽

Contractile Response ◽

Cross Bridge ◽

Kinase C

Tumour-promoting phorbol esters induce slow, sustained contractions of vascular smooth muscle, suggesting that protein kinase C (PKC) may play a role in the regulation of smooth muscle contractility. In some cases, e.g., ferret aortic smooth muscle, phorbol ester induced contractions occur without a change in [Ca2+]i or myosin phosphorylation. Direct evidence for the involvement of PKC came from the use of single saponin-permeabilized ferret aortic cells. A constitutively active catalytic fragment of PKC induced a slow, sustained contraction similar to that triggered by phenylephrine. Both responses were abolished by a peptide inhibitor of PKC. Contractions of similar magnitude occurred even when the [Ca2+] was reduced to close to zero, implicating a Ca2+-independent isoenzyme of PKC. Of the two Ca2+-independent PKC isoenzymes, ε and ζ, identified in ferret aorta, PKCε is more likely to mediate the contractile response because (i) PKCε, but not PKCζ, is responsive to phorbol esters; (ii) upon stimulation with phenylephrine, PKCε translocates from the sarcoplasm to the sarcolemma, whereas PKCζ translocates from a perinuclear localization to the interior of the nucleus; and (iii) when added to permeabilized single cells of the ferret aorta at pCa 9, PKCε, but not PKCζ, induced a contractile response similar to that induced by phenylephrine. A possible substrate of PKCε is the smooth muscle specific, thin filament associated protein, calponin. Calponin is phosphorylated in intact smooth muscle strips in response to carbachol, endothelin-1, phorbol esters, or okadaic acid. Phosphorylation of calponin in vitro by PKC (a mixture of α, β, and γ isoenzymes) dramatically reduces its affinity for F-actin and alleviates its inhibition of the cross-bridge cycling rate. Calponin is phosphorylated in vitro by PKCε but is a very poor substrate of PKCζ. A signal transduction pathway is proposed to explain Ca2+-independent contraction of ferret aorta whereby extracellular signals trigger diacylglycerol production without a Ca2+ transient. The consequent activation of PKCε would result in calponin phosphorylation, its release from the thin filaments, and alleviation of inhibition of cross-bridge cycling. Slow, sustained contraction then results from a slow rate of cross-bridge cycling because of the basal level of myosin light chain phosphorylation (≈0.1 mol Pi/mol light chain). We also suggest that signal transduction through PKCε is a component of contractile responses triggered by agonists that activate phosphoinositide turnover; this may explain why smooth muscles often develop more force in response, e.g., to α1-adrenergic agonists than to K+.Key words: smooth muscle, protein kinase C, calponin.

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