Activation of endogenous c-Src or a related tyrosine kinase by intracellular (pY)EEI peptide increases voltage-operated calcium channel currents in rabbit ear artery cells

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Src-family tyrosine kinases and the Ca2+ signal

In this review, we shall describe the rich crosstalk between non-receptor Src-family kinases (SFKs) and the Ca²⁺ transient generated in activated cells by a variety of extracellular and intracellular stimuli, resulting in diverse signaling events. The exchange of information between SFKs and Ca²⁺ is reciprocal, as it flows in both directions. These kinases are main actors in pathways leading to the generation of the Ca²⁺ signal, and reciprocally, the Ca²⁺ signal modulates SFKs activity and functions. We will cover how SFKs participate in the generation of the cytosolic Ca²⁺ rise upon activation of a series of receptors and the mechanism of clearance of this Ca²⁺ signal. The role of SFKs modulating Ca²⁺-translocating channels participating in these events will be amply discussed. Finally, the role of the Ca²⁺ sensor protein calmodulin on the activity of c-Src, and potentially on other SFKs, will be outlined as well. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Src Kinases Regulate Glutamatergic Input to Hypothalamic Presympathetic Neurons and Sympathetic Outflow in Hypertension

The elevated sympathetic outflow associated with hypertension is maintained by increased N-methyl-d-aspartate receptor (NMDAR) activity in the paraventricular nucleus (PVN) of the hypothalamus. Synaptic NMDAR activity is tightly regulated by protein kinases, including the Src family of tyrosine kinases. We determined whether Src kinases play a role in increased NMDAR activity of PVN neurons projecting to the rostral ventrolateral medulla and in elevated sympathetic vasomotor tone in spontaneously hypertensive rats (SHRs). The Src protein level in the PVN was significantly greater in SHRs than in normotensive Wistar-Kyoto (WKY) rats and was not significantly altered by lowering blood pressure with celiac ganglionectomy in SHRs. Inhibition of Src kinase activity with 4-amino-5-(4-chlorophenyl)-7-(dimethylethyl)pyrazolo[3,4-d]pyrimidine (PP2) completely normalized the higher amplitudes of evoked NMDAR-mediated excitatory postsynaptic currents and puff NMDA-elicited currents of rostral ventrolateral medulla-projecting PVN neurons in SHRs. PP2 treatment also attenuated the higher frequency of NMDAR-mediated miniature excitatory postsynaptic currents of these neurons in SHRs. However, PP2 had no effect on NMDAR-excitatory postsynaptic currents or miniature excitatory postsynaptic currents of rostral ventrolateral medulla-projecting PVN neurons in WKY rats. NMDAR activity increased by an Src-activating peptide was blocked by PP2 but not by inhibition of casein kinase 2. In addition, microinjection of PP2 into the PVN not only decreased lumbar sympathetic nerve discharges and blood pressure but also eliminated the inhibitory effect of the NMDAR antagonist on sympathetic nerve activity and blood pressure in SHRs. Collectively, our findings suggest that increased Src kinase activity potentiates presynaptic and postsynaptic NMDAR activity in the PVN and sympathetic vasomotor tone in hypertension.

Regulation of L-type calcium channel sparklet activity by c-Src and PKC-α

The activity of persistent Ca²⁺ sparklets, which are characterized by longer and more frequent channel open events than low-activity sparklets, contributes substantially to steady-state Ca²⁺ entry under physiological conditions. Here, we addressed two questions related to the regulation of Ca²⁺ sparklets by PKC-α and c-Src, both of which increase whole cell Cav1.2 current: 1) Does c-Src activation enhance persistent Ca²⁺ sparklet activity? 2) Does PKC-α activate c-Src to produce persistent Ca²⁺ sparklets? With the use of total internal reflection fluorescence microscopy, Ca²⁺ sparklets were recorded from voltage-clamped tsA-201 cells coexpressing wild-type (WT) or mutant Cav1.2c (the neuronal isoform of Cav1.2) constructs ± active or inactive PKC-α/c-Src. Cells expressing Cav1.2c exhibited both low-activity and persistent Ca²⁺ sparklets. Persistent Ca²⁺ sparklet activity was significantly reduced by acute application of the c-Src inhibitor PP2 or coexpression of kinase-dead c-Src. Cav1.2c constructs mutated at one of two COOH-terminal residues (Y²¹²²F and Y²¹³⁹F) were used to test the effect of blocking putative phosphorylation sites for c-Src. Expression of Y²¹²²F but not Y²¹³⁹F Cav1.2c abrogated the potentiating effect of c-Src on Ca²⁺ sparklet activity. We could not detect a significant change in persistent Ca²⁺ sparklet activity or density in cells coexpressing Cav1.2c + PKC-α, regardless of whether WT or Y²¹²²F Cav1.2c was used, or after PP2 application, suggesting that PKC-α does not act upstream of c-Src to produce persistent Ca²⁺ sparklets. However, our results indicate that persistent Ca²⁺ sparklet activity is promoted by the action of c-Src on residue Y²¹²² of the Cav1.2c COOH terminus.

The effect of tyrosine nitration of L-type Ca2+ channels on excitation-transcription coupling in colonic inflammation

BACKGROUND AND PURPOSE

Excitation-transcriptional coupling involves communication between plasma membrane ion channels and gene expression in the nucleus. Calcium influx through L-type Ca(2+) channels induces phosphorylation of the transcription factor, cyclic-AMP response element binding protein (CREB) and downstream activation of the cyclic-AMP response element (CRE) promoter regions. Tyrosine nitration of Ca(2+) channels attenuates interactions with c-Src kinase, decreasing Ca(2+) channel currents and smooth muscle contraction during colonic inflammation. In this study we examined the effect of tyrosine nitration and colonic inflammation on Ca(2+) channel mediated phosphorylation of CREB and CRE activation.

EXPERIMENTAL APPROACH

CREB and phospho-CREB were detected by Western blots and CRE activation measured by dual luciferase assay. Chinese hamster ovary (CHO) cells were transfected with hCa(v)1.2b and hCa(v)1.2b c-terminal mutants. Colonic inflammation was induced by intracolonic instillation of 2,4,6 trinitrobenzene sulphonic acid in mouse colon.

KEY RESULTS

In hCa(v)1.2b transfected CHO cells and in native colonic smooth muscle, depolarization with 80 mM KCl induced CREB phosphorylation (pCREB). Treatment with peroxynitrite inhibited KCl-induced pCREB. Following experimental colitis, KCl-induced CREB phosphorylation was abolished in smooth muscle, concomitant with tyrosine nitration of Ca(2+) channels. Depolarization increased CRE activation in hCa(v)1.2b CHO cells by 2.35 fold which was blocked by nifedipine and by protein nitration of Ca(2+) channels with peroxynitrite. The Src-kinase inhibitor, PP2, blocked depolarization-induced CRE activation. Mutation of the C-terminus tyrosine residue, Y2134F, but not Y1861F, blocked CRE activation.

CONCLUSIONS AND IMPLICATIONS

Post-translational modification of Ca(2+) channels due to tyrosine nitration modified excitation-transcriptional coupling in colonic inflammation.

The NADPH oxidase inhibitor diphenyleneiodonium is also a potent inhibitor of cholinesterases and the internal Ca(2+) pump

BACKGROUND AND PURPOSE

Diphenyleneiodonium (DPI) is often used as an NADPH oxidase inhibitor, but is increasingly being found to have unrelated side effects. We investigated its effects on smooth muscle contractions and the related mechanisms.

EXPERIMENTAL APPROACH

We studied isometric contractions in smooth muscle strips from bovine trachea. Cholinesterase activity was measured using a spectrophotometric assay; internal Ca(2+) pump activity was assessed by Ca(2+) uptake into smooth muscle microsomes.

KEY RESULTS

Contractions to acetylcholine were markedly enhanced by DPI (10(-4) M), whereas those to carbachol (CCh) were not, suggesting a possible inhibition of cholinesterase. DPI markedly suppressed contractions evoked by CCh, KCl and 5-HT, and also unmasked phasic activity in otherwise sustained responses. Direct biochemical assays confirmed that DPI was a potent inhibitor of acetylcholinesterase and butyrylcholinesterase (IC(50) approximately 8 x 10(-6) M and 6 x 10(-7) M, respectively), following a readily reversible, mixed non-competitive type of inhibition. The inhibitory effects of DPI on CCh contractions were not mimicked by another NADPH oxidase inhibitor (apocynin), nor the Src inhibitors PP1 or PP2, ruling out an action through the NADPH oxidase signalling pathway. Several features of the DPI-mediated suppression of agonist-evoked responses (i.e. suppression of peak magnitudes and unmasking of phasic activity) are similar to those of cyclopiazonic acid, an inhibitor of the internal Ca(2+) pump. Direct measurement of microsomal Ca(2+) uptake revealed that DPI modestly inhibits the internal Ca(2+) pump.

CONCLUSIONS AND IMPLICATIONS

DPI inhibits cholinesterase activity and the internal Ca(2+) pump in tracheal smooth muscle.

Src family tyrosine kinases mediate contraction of rat isolated tail arteries in response to a hyposmotic stimulus

OBJECTIVE

Hypotonic solutions cause vasoconstriction in rat tail arteries, due largely to activation of L-type calcium channels (CaV1.2). We studied possible roles of tyrosine kinases, particularly src family kinases (SFK) and extracellular signal-related kinases (ERK1/2), in this response.

METHODS

Rat tail arteries were mounted on a myograph for measurement of isometric force. Arteries were bathed in isosmotic physiological saline solution (300 mOsm/l) containing 50 mmol/l mannitol and were stimulated by a hyposmotic solution containing 0 mmol/l mannitol (PSS-M). Activation of tyrosine kinases and ERK1/2 by hyposmotic solution was examined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and western blotting on rat tail artery lysates with specific phospho-antibodies.

RESULTS

Western blotting showed SFK src and yes present in rat tail artery. PSS-M increased tyrosine phosphorylation of several proteins, including SFK and ERK1/2. Genistein blocked phosphorylation of SFK and ERK1/2 by PSS-M. In isolated arteries PSS-M caused a contraction inhibited by the tyrosine kinase inhibitor, genistein, and three structurally different selective SFK inhibitors, herbimycin-A, PP1 and SU6656. Mitogen-activated protein kinase kinase inhibitor PD98059 or selective inhibitors of platelet-derived growth factor receptor (AG1296) and epidermal growth factor receptor (AG1478) had no effect on contraction induced by a hypotonic solution.

CONCLUSIONS

Hyposmotic conditions activate SFK, src and yes, and contract rat tail artery by a SFK-dependent mechanism. ERK1/2 are activated by the hypotonic solution, but do not play a role in the contractile response. SFK modulation of CaV1.2 may be an important mechanism mediating vasoconstriction to mechanical stimuli in vascular smooth muscle.

COOH-terminal association of human smooth muscle calcium channel Ca(v)1.2b with Src kinase protein binding domains: effect of nitrotyrosylation

The carboxyl terminus of the calcium channel plays an important role in the regulation of calcium entry, signal transduction, and gene expression. Potential protein-protein interaction sites within the COOH terminus of the L-type calcium channel include those for the SH3 and SH2 binding domains of c-Src kinase that regulates calcium currents in smooth muscle. In this study, we examined the binding sites involved in Src kinase-mediated phosphorylation of the human voltage-gated calcium channel (Ca(v)) 1.2b (hCav1.2b) and the effect of nitrotyrosylation. Cotransfection of human embryonic kidney (HEK)-293 cells with hCa(v)1.2b and c-Src resulted in tyrosine phosphorylation of the calcium channel, which was prevented by nitration of tyrosine residues by peroxynitrite. Whole cell calcium currents were reduced by 58 + 5% by the Src kinase inhibitor PP2 and 64 + 6% by peroxynitrite. Nitrotyrosylation prevented Src-mediated regulation of the currents. Glutathione S-transferase fusion protein of the distal COOH terminus of hCa(v)1.2b (1809-2138) bound to SH2 domain of Src following tyrosine phosphorylation, while binding to SH3 required the presence of the proline-rich motif. Site-directed mutation of Y(2134) prevented SH2 binding and resulted in reduced phosphorylation of hCa(v)1.2b. Within the distal COOH terminus, single, double, or triple mutations of Y(1837), Y(1861), and Y(2134) were constructed and expressed in HEK-293 cells. The inhibitory effects of PP2 and peroxynitrite on calcium currents were significantly reduced in the double mutant Y(1837-2134F). These data demonstrate that the COOH terminus of hCa(v)1.2b contains sites for the SH2 and SH3 binding of Src kinase. Nitrotyrosylation of these sites prevents Src kinase regulation and may be importantly involved in calcium influx regulation during inflammation.

Caveolin-1 reduces osteosarcoma metastases by inhibiting c-Src activity and met signaling

Caveolin-1 (Cav-1) is highly expressed in normal osteoblasts. This article reports that Cav-1 down-regulation is part of osteoblast transformation and osteosarcoma progression and validates its role as oncosuppressor in human osteosarcoma. A survey of 6-year follow-up indicates a better overall survival for osteosarcoma expressing a level of Cav-1 similar to osteoblasts. However, the majority of primary osteosarcoma shows significantly lower levels of Cav-1 than normal osteoblasts. Accordingly, Met-induced osteoblast transformation is associated with Cav-1 down-regulation. In vitro, osteosarcoma cell lines forced to overexpress Cav-1 show reduced malignancy with inhibited anchorage-independent growth, migration, and invasion. In vivo, Cav-1 overexpression abrogates the metastatic ability of osteosarcoma cells. c-Src and c-Met tyrosine kinases, which are activated in osteosarcoma, colocalize with Cav-1 and are inhibited on Cav-1 overexpression. Thus, Cav-1 behaves as an oncosuppressor in osteosarcoma. Altogether, data suggest that Cav-1 down-modulation might function as a permissive mechanism, which, by unleashing c-Src and Met signaling, enables osteosarcoma cells to invade neighboring tissues. These data strengthen the rationale to target c-Src family kinases and/or Met receptor to improve the extremely poor prognosis of metastatic osteosarcoma.

Different kinases regulate activation of voltage-dependent calcium channels by depolarization in GH3 cells

The L-type Ca2+ channel is the primary voltage-dependent Ca2+-influx pathway in many excitable and secretory cells, and direct phosphorylation by different kinases is one of the mechanisms involved in the regulation of its activity. The aim of this study was to evaluate the participation of Ser/Thr kinases and tyrosine kinases (TKs) in depolarization-induced Ca2+ influx in the endocrine somatomammotrope cell line GH3. Intracellular Ca2+ concentration ([Ca2+]i) was measured using a spectrofluorometric method with fura 2-AM, and 12.5 mM KCl (K+) was used as a depolarization stimulus. K+ induced an abrupt spike (peak) in [Ca2+]i that was abolished in the presence of nifedipine, showing that K+ enhances [Ca2+]i, preferably activating L-type Ca2+ channels. H89, a selective PKA inhibitor, significantly reduced depolarization-induced Ca2+ mobilization in a concentration-related manner when it was applied before or after K+, and okadaic acid, an inhibitor of Ser/Thr phosphatases, which has been shown to regulate PKA-stimulated L-type Ca2+ channels, increased K+-induced Ca2+ entry. When PKC was activated by PMA, the K+-evoked peak in [Ca2+]i, as well as the plateau phase, was significantly reduced, and chelerythrine (a PKC inhibitor) potentiated the K+-induced increase in [Ca2+]i, indicating an inhibitory role of PKC in voltage-dependent Ca2+ channel (VDCC) activity. Genistein, a TK inhibitor, reduced the K+-evoked increase in [Ca2+]i, but, unexpectedly, the tyrosine phosphatase inhibitor orthovanadate reduced not only basal Ca2+ levels but, also, Ca2+ influx during the plateau phase. Both results suggest that different TKs may act differentially on VDCC activation. Activation of receptor TKs with epidermal growth factor (EGF) or vascular endothelial growth factor potentiated K+-induced Ca2+ influx, and AG-1478 (an EGF receptor inhibitor) decreased it. However, inhibition of the non-receptor TK pp60 c-Src enhanced K+-induced Ca2+ influx. The present study strongly demonstrates that a complex equilibrium among different kinases and phosphatases regulates VDCC activity in the pituitary cell line GH3: PKA and receptor TKs, such as vascular endothelial growth factor receptor and EGF receptor, enhance depolarization-induced Ca2+ influx, whereas PKC and c-Src have an inhibitory effect. These kinases modulate membrane depolarization and may therefore participate in the regulation of a plethora of intracellular processes, such as hormone secretion, gene expression, protein synthesis, and cell proliferation, in pituitary cells.

Nitrotyrosylation of Ca2+ Channels Prevents c-Src Kinase Regulation of Colonic Smooth Muscle Contractility in Experimental Colitis

Basal levels of c-Src kinase are known to regulate smooth muscle Ca(2+) channels. Colonic inflammation results in attenuated Ca(2+) currents and muscle contraction. Here, we examined the regulation of calcium influx-dependent contractility by c-Src kinase in experimental colitis. Ca(2+)-influx induced contractions were measured by isometric tension recordings of mouse colonic longitudinal muscle strips depolarized by high K(+). The E(max) to CaCl(2) was significantly less in inflamed tissues (38.4 +/- 7.6%) than controls, indicative of reduced Ca(2+) influx. PP2 [4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine], a selective Src kinase inhibitor, significantly reduced the contractile amplitude and shifted the pD(2) from 3.88 to 2.44 in controls, whereas it was ineffective in inflamed tissues (3.66 versus 3.43). After pretreatment with a SIN-1 (3-morpholinosydnonimine)/peroxynitrite combination, the maximal contraction to CaCl(2) was reduced by 46 +/- 7% in controls but unaffected in inflamed tissues (13 +/- 11%). Peroxynitrite also prevented the inhibitory effect of PP2 in control tissues. In colonic single smooth muscle cells, PP2 inhibited Ca(2+) currents by 84.1 +/- 3.9% in normal but only 36.2 +/- 13% in inflamed tissues. Neither the Ca(2+) channel Ca(v)1.2b, gene expression, nor the c-Src kinase activity was altered by inflammation. Western blot analysis showed no change in the Ca(2+) channel protein expression but increased nitrotyrosylated-Ca(2+) channel proteins during inflammation. These data suggest that post-translational modification of Ca(2+) channels during inflammation, possibly nitrotyrosylation, prevents c-Src kinase regulation resulting in decreased Ca(2+) influx.

CD99 isoforms dictate opposite functions in tumour malignancy and metastases by activating or repressing c-Src kinase activity

CD99 gene encodes two distinct proteins, produced by alternative splicing of CD99 gene transcript. Full-length CD99 isoform (CD99wt) is formed by an extracellular domain, followed by a transmembrane domain and a 36 amino-acid intracytoplasmic domain, which is partially deleted in the truncated, short form (CD99sh). A differential expression of these two CD99 molecules can lead to distinct functional outcomes in lymphocytes. To investigate the functional effects of CD99 molecules on malignancy, forced overexpression of the two CD99 isoforms was induced in osteosarcoma and prostate cancer cells. The two isoforms exhibited opposite functions: the major form dramatically inhibits anchorage-independent growth, anoikis resistance, migration and metastasis, whereas the CD99sh remarkably favours the phenomena. A mechanistic analysis of CD99-transfected osteosarcoma cells points to involvement of c-Src family kinase activity in regulating CD99 functions in malignancy. Ser168 residue of CD99 plays a pivotal role in the reversion of the malignant phenotype. Our findings highlight the involvement of CD99 in crucial processes of cancer malignancy, serving as a curtain raiser for this, so far neglected molecule. In addition, a dualistic role for the two CD99 isoforms was shown in agreement with what was observed for other cell adhesion molecules.

Integrin Receptor Activation Triggers Converging Regulation of Cav1.2 Calcium Channels by c-Src and Protein Kinase A Pathways

L-type, voltage-gated Ca2+ channels (CaL) play critical roles in brain and muscle cell excitability. Here we show that currents through heterologously expressed neuronal and smooth muscle CaL channel isoforms are acutely potentiated following alpha5beta1 integrin activation. Only the alpha1C pore-forming channel subunit is critical for this process. Truncation and site-directed mutagenesis strategies reveal that regulation of Cav1.2 by alpha5beta1 integrin requires phosphorylation of alpha1C C-terminal residues Ser1901 and Tyr2122. These sites are known to be phosphorylated by protein kinase A (PKA) and c-Src, respectively, and are conserved between rat neuronal (Cav1.2c) and smooth muscle (Cav1.2b) isoforms. Kinase assays are consistent with phosphorylation of these two residues by PKA and c-Src. Following alpha5beta1 integrin activation, native CaL channels in rat arteriolar smooth muscle exhibit potentiation that is completely blocked by combined PKA and Src inhibition. Our results demonstrate that integrin-ECM interactions are a common mechanism for the acute regulation of CaL channels in brain and muscle. These findings are consistent with the growing recognition of the importance of integrin-channel interactions in cellular responses to injury and the acute control of synaptic and blood vessel function.

Involvement of Src tyrosine kinase and mitogen-activated protein kinase in the facilitation of calcium channels in rat nucleus of the tractus solitarius by angiotensin II

It is recognized that brain contains all the components of the renin-angiotensin systems (RAS). The nucleus of the tractus solitarius (NTS) is known to play a major role in the regulation of cardiovascular, respiratory, gustatory, hepatic and swallowing functions. Voltage-dependent Ca2+ channels (VDCCs) serve as crucial mediators of membrane excitability and Ca2+-dependent functions such as neurotransmitter release, enzyme activity and gene expression. The purpose of this study was to investigate the effects of angiotensin II (Ang II) on VDCC currents (I(Ca)) in the NTS using patch-clamp recording methods. An application of Ang II caused facilitation of L-type I(Ca) in a concentration-dependent manner with an EC50 of 167 nm and a Hill coefficient of 1.73. AT1 receptor antagonist losartan antagonized the Ang II-induced facilitation of I(Ca). Intracellular dialysis of the Galpha(i)-protein antibody attenuated the Ang II-induced facilitation of I(Ca). Both Src tyrosine kinase inhibitor and mitogen-activated protein kinase (MAPK) inhibitor attenuated the Ang II-induced facilitation of I(Ca). p38 MAPK inhibitor also attenuated the Ang II-induced facilitation of I(Ca). These results indicate that Ang II facilitates L-type VDCCs via Galpha(i)-proteins involving Src tyrosine kinase and p38 MAPK kinase mediated by AT1 receptors in NTS.

Protein and gene expression of Ca2+ channel isoforms in murine colon: effect of inflammation

L-Type voltage-dependent Ca2+ channels (L-VDCC) mediate calcium influx in response to membrane depolarization and regulate intracellular processes such as contraction, secretion, neurotransmission, and gene expression. Colonic inflammation significantly attenuates calcium currents in smooth muscle; however, the basis for this remains unclear. In this study we examined the protein and mRNA expression of two isoforms of Ca(v)1.2, encoded by either exon la or 1b. Both isoforms were detected by Western blots, immunohistochemistry and RT-PCR in smooth muscle cells. Neither the protein nor mRNA expression measured by real-time PCR of either isoforms was affected in colonic myocytes from dextran sulfate sodium-treated mice. In whole-cell voltage-clamp experiments, the amplitude of the calcium currents were decreased by almost 70% by inflammation. The calcium channel currents were attenuated by 50 +/- 3% by the c-src kinase specific inhibitor, PP2, in control cells but only 19 +/- 7% in cells from inflamed mice. These studies suggest that decreased calcium channel currents following colonic inflammation are not due to decreased expression but may result from altered regulation by the non-receptor cellular tyrosine kinase, c-src kinase.

Acidosis-induced protein tyrosine phosphorylation depends on Ca2+ influx via voltage-dependent Ca2+ channels in SHR aorta

The contractile response to acidosis in isolated aorta from spontaneously hypertensive rat (SHR) depends upon tyrosine phosphorylation of phosphatidylinositol 3 kinase (PI3-kinase) and Ca2+ influx via voltage-dependent Ca2+ channels (VDCC). In this study, verapamil, a VDCC inhibitor, was shown to markedly inhibit acidic pH-induced contraction, whereas the residual contraction in the presence of verapamil was unaffected by the PI3-kinase inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride (LY-294002). Interestingly, the LY-294002-insensitive component of contraction was further inhibited by verapamil in the presence of LY-294002. Western blotting revealed that acidosis stimulated tyrosine phosphorylation of p85, which was abolished when tissues were pretreated with tyrphostin 23, a tyrosine kinase inhibitor, verapamil or EGTA. In fura-2-loaded aortic strips, acidosis induced a rise in intracellular Ca2+ ([Ca2+]i) that was partially inhibited by LY-294002. The residual increase in [Ca2+]i caused by acidosis in the presence of LY-294002 was abolished by verapamil. These findings suggest that acidosis-induced Ca2+ influx through VDCC is the upstream event leading to the tyrosine phosphorylation of PI3-kinase, which in turn contributes to the enhancement of Ca2+ entry to some extent in SHR aorta.

Muscarinic M2 Receptor Stimulation of Cav1.2b Requires Phosphatidylinositol 3-Kinase, Protein Kinase C, and c-Src

This study investigated regulation of L-type calcium channels (Cav1.2b) by acetylcholine (ACh) in rabbit portal vein myocytes. Whole-cell currents were recorded using 5 mmol/L barium as charge carrier. ACh (10 μmol/L) increased peak currents by 40%. This effect was not reversed by the selective muscarinic M3 receptor antagonist 4-DAMP (100 nmol/L) but was blocked by the M2 receptor antagonist methoctramine (5 μmol/L). The classical and novel protein kinase C (PKC) antagonist calphostin C (50 nmol/L) abolished ACh responses, whereas the classical PKC antagonist Gö6976 (200 nmol/L) had no effect. ACh responses were also abolished by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 (20 μmol/L), by the c-Src inhibitor PP2 (10 μmol/L) (but not the inactive analogue PP3), and by dialyzing cells with an antibody to the G-protein subunit Gβγ. Cells dialyzed with c-Src had significantly greater currents than control cells. Current enhancement persisted in the presence of LY294002, suggesting that c-Src is downstream of PI3K. Phorbol 12,13-dibutyrate (PDBu, 0.1 μmol/L) increased currents by 74%. This effect was abolished by calphostin C and reduced by Gö6976. The PDBu response was also reduced by PP2, and the PP2-insensitive component was blocked by Gö6976. In summary, these data suggest that ACh enhances Cav1.2b currents via M2 receptors that couple sequentially to Gβγ, PI3K, a novel PKC, and c-Src. PDBu stimulates the novel PKC/c-Src pathway along with a second pathway that is independent of c-Src and involves a classical PKC.

Molecular dissection of egg fertilization signaling with the aid of tyrosine kinase-specific inhibitor and activator strategies

Fertilization is triggered by sperm-egg interaction and fusion that initiate a transient rise(s) in the free intracellular calcium ([Ca(2+)](i)) that is responsible for a series of biochemical and cell biological events, so-called "egg activation". Calcium-dependent egg activation leads to the initiation of developmental program that culminates in the birth of individuals. A growing body of knowledge has uncovered the molecular mechanisms underlying sperm-induced transient [Ca(2+)](i) increase(s) to some extent; namely, in most animals so far studied, a second messenger inositol 1,4,5-trisphosphate (IP(3)) seems to play a pivotal role in inducing [Ca(2+)](i) transient(s) at fertilization. However, signaling mechanisms used by sperm to initiate IP(3)-[Ca(2+)](i) transient pathway have not been elucidated. To approach this problem, we have employed African clawed frog, Xenopus laevis, as a model animal and conducted experiments designed specifically to determine the role of the Src family protein-tyrosine kinases (SFKs or Src family PTKs) in the sperm-induced egg activation. This review compiles information about the use of PTK-specific inhibitors and activators for analyzing signal transduction events in egg fertilization. Specifically, we focus on molecular identification of Xenopus Src and the signaling mechanism of the Src-dependent egg activation that has been established recently. We also summarize recent advances in understanding the role of the Src family kinases in egg fertilization of other model organisms, and discuss future directions of the field.

Contribution of Src tyrosine kinase to cerebral vasospasm after subarachnoid hemorrhage

OBJECT

Mitogen-activated protein kinase (MAPK) has been implicated in cerebral vasospasm after subarachnoid hemorrhage (SAH). This study was conducted to investigate whether Src tyrosine kinase, an upstream regulator of MAPK, is involved in cerebral vasospasm.

METHODS

An established canine double-hemorrhage model was used. Twenty-four dogs were divided into four groups: control, vehicle-treated, Src inhibitor PP2-treated, and Src inhibitor damnacanthal-treated groups. Vehicle (dimethyl sulfoxide), PP2, or damnacanthal was injected daily into the cisterna magna of 18 dogs at 3 to 6 days after induction of SAH. Angiography was performed on Day 0 (the day on which the first blood injection was administered to induce SAH) and on Day 7. Western blot analysis of Src and MAPK activation in basilar arteries (BAs) collected on Day 7 post-SAH was performed. Severe vasospasm was observed in the BAs of vehicle-treated dogs. Mild vasospasm was observed in all dogs treated with Src inhibitors. Phosphorylated Src and MAPK were increased after SAH and activation of these kinases in the BAs was abolished by PP2 and damnacanthal.

CONCLUSIONS

The tyrosine kinase Src is an important upstream regulator of MAPK, and inhibition of Src might offer a new therapy in the management of cerebral vasospasm.

Increased tyrosine phosphorylation of alpha(1C) subunits of L-type voltage-gated calcium channels and interactions among Src/Fyn, PSD-95 and alpha(1C) in rat hippocampus after transient brain ischemia

It has been reported that the Src family kinases-mediated tyrosine phosphorylation of alpha(1C) subunits of L-type voltage-gated calcium channels (L-VGCCs) potentiates the channel currents. In this study, we evaluated the alterations in the tyrosine phosphorylation level of alpha(1C) and in the interactions involving Src/Fyn, alpha(1C) and PSD-95 in the hippocampus after transient (15 min) brain ischemia followed by various times of reperfusion using immunoprecipitation and immunoblotting. Transient brain ischemia was induced by the method of four-vessel occlusion in Sprague-Dawley rats. The tyrosine phosphorylation level of alpha(1C) subunits elevated immediately after brain ischemia. The elevation in phosphorylation sustained for at least 6 h and peaked at 15 min of reperfusion. Transient brain ischemia and reperfusion also caused rapid and sustained increases in the interactions of Src and Fyn with alpha(1C) subunits. More interestingly, co-immunoprecipitation analysis showed that 15 min of reperfusion dramatically increased the interaction between PSD-95 and alpha(1C) and promoted the formation of alpha(1C)-PSD-95-Src complexes, for the first time. The protein levels of alpha(1C), Src, Fyn and PSD-95 showed no differences at all time points. These results suggest a novel mechanism involving the ischemia/reperfusion-induced recruitment of L-VGCCs, Src and Fyn to the PSD-95 signaling complex that facilitates the tyrosine phosphorylation of alpha(1C) subunits by Src family kinases and may contribute to the up-regulation of L-VGCCs activity in postischemic hippocampus.

L-type voltage-gated calcium channel attends regulation of tyrosine phosphorylation of NMDA receptor subunit 2A induced by transient brain ischemia

To study the mechanism of the L-type voltage-gated calcium channel (L-VGCC) involved in neuronal injury induced by brain ischemia and reperfusion (I/R), transient (15 min) brain ischemia was induced by four-vessel occlusion of Sprague-Dawley (SD) rats. Tyrosine phosphorylation of NR2A and interaction of NR2A with Src and Pyk2 in hippocampus induced by brain ischemia and reperfusion (I/R) were determined by immunoprecipitation and immunoblot(ting). Tyrosine phosphorylation of NR2A in hippocampus was enhanced after I/R. Interaction of NR2A with Src and Pyk2, tyrosine phosphorylation and kinase activity of Src and Pyk2 also increased after I/R. All the increases were partly inhibited by L-VGCC antagonist nifedipine administered to rats 20 min prior to brain ischemia. The results suggested that increase of tyrosine phosphorylation of NR2A induced by I/R had a relation to activation of L-VGCC. Src and Pyk2 interacting with NR2A might also be involved in this regulation of the tyrosine phosphorylation of NR2A induced by I/R.

Genistein inhibits cardiac L-type Ca(2+) channel activity by a tyrosine kinase-independent mechanism

It has been suggested that protein tyrosine kinase (PTK) activity can directly regulate cardiac L-type Ca(2+) channels. This conclusion is based to a large extent on the observation that the PTK inhibitor genistein can inhibit the cardiac L-type Ca(2+) current. The purpose of the present study was to determine whether the ability of genistein to inhibit cardiac L-type Ca(2+) channel activity is due to inhibition of PTK activity. Genistein significantly reduced the magnitude of the L-type Ca(2+) current in guinea pig ventricular myocytes recorded using the whole-cell patch-clamp technique. However, this effect was associated with extracellular, not intracellular, application of the drug. Peroxovanadate (PVN), a potent protein tyrosine phosphatase inhibitor, had no effect on the basal Ca(2+) current. PVN was also ineffective in preventing the inhibitory effect of genistein. Internal perfusion of cells with a pipette solution containing ATPgammaS was used to prevent reversibility of phosphorylation-dependent processes. This treatment did not alter the inhibitory effect of genistein, although it did result in irreversible protein kinase A-dependent regulation of the Ca(2+) current. Bath application of lavendustin A, a PTK inhibitor that is structurally unrelated to genistein, did not affect the Ca(2+) current amplitude. The inhibitory effect of genistein was also associated with a hyperpolarizing shift in the voltage dependence of Ca(2+) channel inactivation. These results are consistent with the conclusion that the cardiac L-type Ca(2+) current is not directly regulated by PTK activity and that the inhibitory effect of genistein is due to direct non-catalytic blockade of the channels.

Stimulation of L-type Ca(2+) channels by increase of intracellular InsP3 in rat retinal pigment epithelial cells

The purpose of this study was to investigate the role of voltage-dependent L-type Ca(2+)channels in intracellular Ca(2+)signaling of the retinal pigment epithelium (RPE). Patch-clamp techniques in conjunction with measurements of the intracellular free Ca(2+)using the Ca(2+)-sensitive fluorescence dye fura-2 were performed using cultured rat RPE cells. Intracellular application of inositol-1,4,5-trisphosphate (InsP3; 10 microM) via the patch-pipette during the whole-cell configuration led to an increase in the intracellular free Ca(2+)([Ca(2+)](i)). This effect could be reduced by the L-type Ca(2+)channel blocker nifedipine (2 microM). At the moment of the maximal rise in [Ca(2+)](i)L-type currents displayed an increase in the current density and shifts in the activation curve and of the steady-state inactivation. Comparable changes of L-type channel activity could be observed by induction of capacitative Ca(2+)entry, a maneuver to release Ca(2+)from intracellular Ca(2+)stores independently from InsP3. The increase in L-type Ca(2+)channel activity and [Ca(2+)](i)by intracellular application of InsP3 or induction of capacitative Ca(2+)entry could be inhibited by blocking tyrosine kinase activity using genistein (5 microM) or tyrphostin 51 (10 microM). It is concluded that L-type Ca(2+)channels are involved in the Ca(2+)/InsP3 second messenger system by generating an influx of extracellular Ca(2+)into the cell. This is enabled by depletion of cytosolic Ca(2+)stores and tyrosine kinase-dependent activation of L-type channels.

Regulation of cardiac and smooth muscle Ca(2+) channels (Ca(V)1.2a,b) by protein kinases

High voltage-activated Ca(2+) channels of the Ca(V)1.2 class (L-type) are crucial for excitation-contraction coupling in both cardiac and smooth muscle. These channels are regulated by a variety of second messenger pathways that ultimately serve to modulate the level of contractile force in the tissue. The specific focus of this review is on the most recent advances in our understanding of how cardiac Ca(V)1.2a and smooth muscle Ca(V)1.2b channels are regulated by different kinases, including cGMP-dependent protein kinase, cAMP-dependent protein kinase, and protein kinase C. This review also discusses recent evidence regarding the regulation of these channels by protein tyrosine kinase, calmodulin-dependent kinase, purified G protein subunits, and identification of possible amino acid residues of the channel responsible for kinase regulation.

Regulation of ion channels by protein tyrosine phosphorylation

Ion channels are regulated by protein phosphorylation and dephosphorylation of serine, threonine, and tyrosine residues. Evidence for the latter process, tyrosine phosphorylation, has increased substantially since this topic was last reviewed. In this review, we present a comprehensive summary and synthesis of the literature regarding the mechanism and function of ion channel regulation by protein tyrosine kinases and phosphatases. Coverage includes the majority of voltage-gated, ligand-gated, and second messenger-gated channels as well as several types of channels that have not yet been cloned, including store-operated Ca2+ channels, nonselective cation channels, and epithelial Na+ and Cl- channels. Additionally, we discuss the critical roles that channel-associated scaffolding proteins may play in localizing protein tyrosine kinases and phosphatases to the vicinity of ion channels.

Regulation of the L-type calcium channel by alpha 5beta 1 integrin requires signaling between focal adhesion proteins

The L-type calcium channel is the major calcium influx pathway in vascular smooth muscle and is regulated by integrin ligands, suggesting an important link between extracellular matrix and vascular tone regulation in tissue injury and remodeling. We examined the role of integrin-linked tyrosine kinases and focal adhesion proteins in regulation of L-type calcium current in single vascular myocytes. Soluble tyrosine kinase inhibitors blocked the increase in current produced by alpha(5) integrin antibody or fibronectin, whereas tyrosine phosphatase inhibition enhanced the effect. Cell dialysis with an antibody to focal adhesion kinase or with FRNK, the C-terminal noncatalytic domain of focal adhesion kinase, produced moderate (24 or 18%, respectively) inhibition of basal current but much greater inhibition (63 or 68%, respectively) of integrin-enhanced current. A c-Src antibody and peptide inhibitors of the Src homology-2 domain or a putative Src tyrosine phosphorylation site on the channel produced similar inhibition. Antibodies to the cytoskeletal proteins paxillin and vinculin, but not alpha-actinin, inhibited integrin-dependent current by 65-80%. Therefore, alpha(5)beta(1) integrin appears to regulate a tyrosine phosphorylation cascade involving Src and various focal adhesion proteins that control the function of the L-type calcium channel. This interaction may represent a novel mechanism for control of calcium influx in vascular smooth muscle and other cell types.

Integrins and mechanotransduction of the vascular myogenic response

This review summarizes what is currently known about the role of integrins in the vascular myogenic response. The myogenic response is the rapid and maintained constriction of a blood vessel in response to pressure elevation. A role for integrins in this process has been suggested because these molecules form an important mechanical link between the extracellular matrix and the vascular smooth muscle cytoskeleton. We briefly summarize evidence for a general role of integrins in mechanotransduction. We then describe the integrin subunit combinations known to exist in smooth muscle and the vascular wall matrix proteins that may interact with these integrins. We then discuss the effects of integrin-specific peptides and antibodies on vascular tone and on calcium entry mechanisms in vascular smooth muscle. Because integrin function is linked to the cytoskeleton, we discuss evidence for the role of the cytoskeleton in determining myogenic responsiveness. Finally, we analyze evidence that integrin-linked signaling pathways, such as those involving protein tyrosine phosphorylation cascades and mitogen-activated protein kinases, are required for myogenic tone.

Role of c-Src in the regulation of vascular contraction and Ca2+ signaling by angiotensin II in human vascular smooth muscle cells

OBJECTIVE

Tyrosine kinases, typically associated with growth-signaling pathways, also play a role in Ang II-stimulated vascular contraction. However the specific kinases involved are unclear. We hypothesize here that c-Src, a non-receptor tyrosine kinase, is an important upstream regulator of vascular smooth muscle cell (VSMC) Ca2+ signaling and associated vascular contraction induced by Ang II.

METHODS

Cultured VSMCs from resistance arteries of healthy subjects were studied. Human VSMCs electroporated with anti-c-Src antibody and c-Src-deficient VSMCs from small arteries of c-Src knockout mice (Src-/-mVSMCs) were also investigated. Intracellular free Ca2+ concentration ([Ca2+]i), c-Src activity and IP3 production were measured by fura 2, immunoblot and radioimmunoassay respectively. Contraction was examined in intact rat small arteries.

RESULTS

Ang II rapidly increased VSMC c-Src activity, with peak responses obtained at 1 min. Ang II induced a biphasic [Ca2+]i response (Emax = 636 +/- 123 nmol/l). The initial [Ca2+]i transient, mediated primarily by Ca2+mobilization, was dose-dependently attenuated by the selective Src inhibitor, PP2, but not by PP3 (inactive analogue). Ang II-elicited [Ca2+]i responses were blunted in cells electroporated with anti-c-Src antibodies and in c-Src-/-mVSMCs. Src inhibition decreased Ang II-induced generation of IP3 in human VSMCs. Ang II dose-dependently increased vascular contraction (Emax = 40 +/- 6.5%). These responses were attenuated by PP2 (Emax = 7.8 +/- 0.08%) but not by PP3 (Emax = 35 +/- 4.5%).

CONCLUSIONS

Our findings identify c-Src as an important regulator of VSMC [Ca2+]i signaling and implicate a novel contractile role for this non-receptor tyrosine kinase in Ang II-stimulated vascular smooth muscle.

Potentiation of neuronal L calcium channels by IGF-1 requires phosphorylation of the alpha1 subunit on a specific tyrosine residue

Insulin-like growth factor 1 (IGF-1) rapidly potentiates N and L calcium channel currents in cerebellar granule neurons by an unknown mechanism. Here, we show that the L channel alpha1C subunit is tyrosine phosphorylated in response to IGF-1. Moreover, expression of kinase-dead c-Src in neurons or acute block of Src family kinases with a cell-permeable inhibitor specifically blocks L channel potentiation. Purified Src kinase phosphorylates tyrosine residue Y2122 of the C terminus of neuronal alpha1C in vitro, and c- and v-Src directly bind the C terminus. When expressed in neuroblastoma cells, point mutation of Y2122 prevents both tyrosine phosphorylation of alpha1C and IGF-1 potentiation. Our data provide a biochemical mechanism whereby phosphorylation of a single specific tyrosine residue rapidly modifies ion channel physiology.

Specific inhibition of stretch-induced increase in L-type calcium channel currents by herbimycin A in canine basilar arterial myocytes

The effects of protein-tyrosine kinase (PTK) and protein-tyrosine phosphatase (PTP) inhibitors on voltage-activated barium currents (I(Ba)) through L-type calcium channels increased by hypotonic solution were investigated in canine basilar arterial myocytes by the whole-cell patch-clamp technique. I(Ba) was elicited by depolarizing step from a holding potential of -80 to +10 mV and identified by using an L-type calcium channel agonist, Bay K 8644 (100 nM), and an L-type calcium channel blocker, nicardipine (1 microM). Hypotonic superfusate induced cell swelling and acted as a stretch stimulus, which reversibly increased peak I(Ba) amplitude at +10 mV. I(Ba) was also decreased by nicardipine (1 microM) under the hypotonic condition. PTK inhibitors such as herbimycin A (30 nM), genistein (10 microM), and lavendustin A (10 microM) decreased I(Ba) enhanced by hypotonic solution. Genistein also decreased I(Ba) in a concentration-dependent manner under the isotonic condition. The inactive genistein analogue daidzein (10 microM) had no effect on I(Ba) under either the isotonic or hypotonic condition. By contrast, herbimycin A did not decrease I(Ba) under the isotonic condition. Sodium orthovanadate (10 microM), a PTP inhibitor, increased I(Ba) under both conditions. The present results suggest that cell swelling by hypotonic solution increases the L-type calcium channel currents in canine basilar artery and that herbimycin-sensitive PTK activity is primarily involved in the enhancement of calcium channel currents.

Attenuation of pressure-induced myogenic contraction and tyrosine phosphorylation by fasudil, a cerebral vasodilator, in rat cerebral artery

The mechanism by which fasudil inhibits pressure-induced myogenic contraction was studied with regard to tyrosine phosphorylation in rat cerebral artery. Intracellular Ca(2+) concentration ([Ca(2+)](i)) and vessel diameter were simultaneously measured. Total tyrosine phosphorylation level and phosphorylation of tyrosine 419 on pp60(src) required for its full catalytic activity were immunocytochemically detected in situ. Fasudil (1 - 100 microM) partially suppressed the increase in [Ca(2+)](i), and totally attenuated contraction elicited by pressurization from 10 to 60 mmHg. Furthermore, fasudil (100 microM) significantly attenuated tyrosine phosphorylation and the activity of pp60(src) augmented in situ by pressure. Herbimycin A (1 - 100 nM) and genistein (3 - 30 microM), tyrosine kinase inhibitors, effectively attenuated the pressure-induced increase in [Ca(2+)](i), contraction, tyrosine phosphorylation, and activation of pp60(src). Both fasudil and herbimycin A directly inhibited the pp60(src) activity in a cell free system. Orthovanadate (100 microM), a tyrosine phosphatase inhibitor, significantly potentiated the pressure-induced increase in [Ca(2+)](i) and contraction. Nicardipine (100 nM), a Ca(2+) antagonist, completely inhibited pressure-induced increase in [Ca(2+)](i) and contraction, but affected neither tyrosine phosphorylation nor activity of pp60(src) in the pressurized arteries. Arginine-glycine-aspartic acid-serine peptide (1 - 100 microM) concentration-dependently reduced the pressure-induced contraction. In addition to the hitherto reported vasodilatory actions of fasudil, the present results suggest the inhibition by fasudil of pressure-induced tyrosine phosphorylation and pp60(src) activation. The wide spectrum of inhibitory actions of fasudil may contribute to the effective attenuation of the pressure-induced contraction in the cerebral artery.

Activation of neuroendocrine L-type channels (alpha1D subunits) in retinal pigment epithelial cells and brain neurons by pp60(c-src)

The aim of this study is to characterize the subtype of tyrosine kinase-regulated L-type Ca(2+) channels in retinal pigment epithelial (RPE) cells. Ca(2+) channel alpha1D-subunits were enriched by immunoprecipitation from membrane proteins isolated from rat RPE cells. Western blot analysis of the precipitates revealed coprecipitation of pp60(c-src). In addition, in precipitates obtained with antibodies against pp60(c-src), alpha1D-subunits were identified. The same was observed in immunoprecipitations from rat brain neurons. Tyrosine phosphorylation of alpha1D-subunits was confirmed using anti-phosphotyrosine antibodies. Ba(2+) currents through L-type channels in cultured rat RPE cells were increased by intracellular application of active pp60(c-src) (30 U/ml) (heat-inactivated pp60(c-src) had no effect). Thus, L-type channels of the neuroendocrine subtype can be expressed in epithelial cells and are activated by tyrosine kinase of the src subtype. This kind of regulation is also suggested for brain-derived neurons.

Effects of protein tyrosine kinase inhibitors on voltage-operated calcium channel currents in vascular smooth muscle cells and pp60(c-src) kinase activity

1. Tyrosine kinases have been proposed as regulators of voltage-operated calcium channels. The effects of a range of structurally different inhibitors of protein tyrosine kinases (PTK) were examined on voltage-operated calcium channel currents (I(Ba)) and pp60(c-src) kinase (c-src) activity in vitro. 2. I(Ba) was measured in single myocytes isolated from rabbit ear artery by conventional whole cell voltage-clamp techniques. The activity of purified human c-src was measured in vitro using a non-radioactive assay. 3. Bath application of tyrphostin-23 and genistein (non-selective PTK inhibitors), bistyrphostin (a receptor-PTK-selective inhibitor) and PP1 (a src family-selective inhibitor) inhibited I(Ba) in a concentration-dependent manner over a range of test membrane potentials. Intracellular application of peptide-A, a peptide inhibitor of c-src also inhibited currents. Inhibitor potency series against I(Ba) was PP1 > genistein > tyrphostin 23 > bistyrphostin. 4. Tyrphostin-23, genistein, PP1, and peptide-A shifted the steady-state inactivation curves in a hyperpolarized direction without altering their slope. The inhibitors had no significant effects on I(Ba) activation calculated from current-voltage relationships. 5. The agents inhibited c-src activity in a concentration-dependent manner. The order of potency was PP1 > genistein > peptide-A > tyrphostin-23 > bistyrphostin. The IC(50) for inhibition of c-src activity was similar to the IC(50) for inhibition of I(Ba) in all cases. 6. Western blot analysis with a specific antibody to c-src showed the presence of this cytoplasmic tyrosine kinase in rabbit ear artery cells. 7. A range of structurally dissimilar inhibitors of PTKs inhibit I(Ba) and c-src activity with similar potency. These data provide further evidence implicating endogenous c-src in the modulation of L-type calcium channels in vascular smooth muscle cells.

Signaling mechanisms underlying the vascular myogenic response

The vascular myogenic response refers to the acute reaction of a blood vessel to a change in transmural pressure. This response is critically important for the development of resting vascular tone, upon which other control mechanisms exert vasodilator and vasoconstrictor influences. The purpose of this review is to summarize and synthesize information regarding the cellular mechanism(s) underlying the myogenic response in blood vessels, with particular emphasis on arterioles. When necessary, experiments performed on larger blood vessels, visceral smooth muscle, and even striated muscle are cited. Mechanical aspects of myogenic behavior are discussed first, followed by electromechanical coupling mechanisms. Next, mechanotransduction by membrane-bound enzymes and involvement of second messengers, including calcium, are discussed. After this, the roles of the extracellular matrix, integrins, and the smooth muscle cytoskeleton are reviewed, with emphasis on short-term signaling mechanisms. Finally, suggestions are offered for possible future studies.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Modulation of calcium current in arteriolar smooth muscle by alphav beta3 and alpha5 beta1 integrin ligands

Vasoactive effects of soluble matrix proteins and integrin-binding peptides on arterioles are mediated by alphav beta3 and alpha5 beta1 integrins. To examine the underlying mechanisms, we measured L-type Ca2+ channel current in arteriolar smooth muscle cells in response to integrin ligands. Whole-cell, inward Ba2+ currents were inhibited after application of soluble cyclic RGD peptide, vitronectin (VN), fibronectin (FN), either of two anti-beta3 integrin antibodies, or monovalent beta3 antibody. With VN or beta3 antibody coated onto microbeads and presented as an insoluble ligand, current was also inhibited. In contrast, beads coated with FN or alpha5 antibody produced significant enhancement of current after bead attachment. Soluble alpha5 antibody had no effect on current but blocked the increase in current evoked by FN-coated beads and enhanced current when applied in combination with an appropriate IgG. The data suggest that alphavbeta3 and alpha5 beta1 integrins are differentially linked through intracellular signaling pathways to the L-type Ca2+ channel and thereby alter control of Ca2+ influx in vascular smooth muscle. This would account for the vasoactive effects of integrin ligands on arterioles and provide a potential mechanism for wound recognition during tissue injury.

Effect of inhibition of tyrosine phosphatases on voltage-operated calcium channel currents in rabbit isolated ear artery cells

1. The effect of increasing cellular tyrosine phosphorylation by inhibiting endogenous tyrosine phosphatases was examined on voltage-operated calcium channel currents in vascular smooth muscle cells. 2. In single ear artery smooth muscle cells of the rabbit, studied by the whole cell voltage clamp technique, intracellular application of the tyrosine phosphatase inhibitors, sodium orthovanadate (100 microM) and peroxyvanadate (100 microM orthovanadate + 1 mM H2O2) increased voltage-operated calcium channel currents by 56% and 83%, respectively. 3. Bath application of two other membrane permeant tyrosine phosphatase inhibitors, phenylarsine oxide (100 microM) and dephostatin (50 microM) also increased voltage-operated calcium channel currents by 48% and 52%, respectively. 4. The selective tyrosine kinase inhibitor, tyrphostin-23 (100 microM) reduced calcium channel currents by 41%. Pre-incubation with tyrphostin-23 abolished the effects of peroxyvanadate, phenylarsine oxide and dephostatin on calcium channels. 5. Western blot analysis of rabbit ear artery cell lysates showed increased tyrosine phosphorylation of several endogenous proteins following treatment with peroxyvanadate. 6. These results indicate that a number of structurally dissimilar inhibitors of tyrosine phosphatases increase voltage-operated calcium channel currents in arterial smooth muscle cells presumably due to increased tyrosine phosphorylation.

Modulation of voltage-dependent Ca2+ channels in rabbit colonic smooth muscle cells by c-Src and focal adhesion kinase

There is emerging evidence indicating that smooth muscle contraction and Ca2+ influx through voltage-dependent L-type Ca2+ channels are regulated by tyrosine kinases; however, the specific kinases involved are largely unknown. In rabbit colonic muscularis mucosae cells, tyrosine-phosphorylated proteins of approximately 60 and 125 kDa were observed in immunoblots using an anti-phosphotyrosine antibody and were identified as c-Src and focal adhesion kinase (FAK) by immunoblotting with specific antibodies. FAK co-immunoprecipitated with c-Src, and the phosphorylation of the c-Src.FAK complex was markedly enhanced by platelet-derived growth factor (PDGF) BB. The presence of activated c-Src in unstimulated cells was identified in cell lysates by immunoblotting with an antibody recognizing the autophosphorylated site (P416Y). In whole-cell patch-clamp studies, intracellular dialysis of a Src substrate peptide and anti-c-Src and anti-FAK antibodies suppressed Ca2+ currents by 60, 62, and 43%, respectively. In contrast, intracellular dialysis of an anti-mouse IgG or anti-Kv1.5 antibody did not inhibit Ca2+ currents. Co-dialysis of anti-c-Src and anti-FAK antibodies inhibited Ca2+ currents (63%) equivalent to dialysis with the anti-c-Src antibody alone. PDGF-BB enhanced Ca2+ currents by 43%, which was abolished by the anti-c-Src and anti-FAK antibodies. Neither the MEK inhibitor PD 098059 nor an anti-Ras antibody inhibited basal Ca2+ currents or PDGF-stimulated Ca2+ currents. The alpha1C subunit of the L-type Ca2+ channel co-immunoprecipitated with anti-c-Src and anti-phosphotyrosine antibodies, indicating direct association of c-Src kinase with the Ca2+ channel. These data suggest that c-Src and FAK, but not the Ras/mitogen-activated protein kinase cascade, modulate basal Ca2+ channel activity and mediate the PDGF-induced enhancement of L-type Ca2+ currents in differentiated smooth muscle cells.