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[[alpha].sub.1]-Aderenoceptor-mediated constriction of rabbit inferior vena cava (IVC) is signaled by asynchronous wavelike [Ca.sup.2+] oscillations in the in situ smooth muscle. We have shown previously that a putative nonselective cationic channel (NSCC) is required for these oscillations. In this report, we show that the application of 2-aminoethoxyphenyl borate (2-APB) to antagonize inositol 1,4,5-trisphosphate (Ins[P.sub.3])-sensitive [Ca.sup.2+] release channels (I[P.sub.3]R channels) can prevent the initiation and abolish ongoing [[alpha].sub.1]-aderenoceptor-mediated tonic constriction of the venous smooth muscle by inhibiting the generation of these intracellular [Ca.sup.2+] concentration ([[[Ca.sup.2 +]].sub.i]) oscillations. The observed effects of 2-APB can only be attributed to its selective inhibition on the I[P.sub.3]R channels, not to its slight inhibition of the L-type voltage-gated [Ca.sup.2+] channel and the sarco(endo)plasmic reticulum [Ca.sup.2+] ATPase. Furthermore, 2-APB had no effect on the ryanodine-sensitive [Ca.sup.2+] release channel and the store-operated channel (SOC) in the IVC. These results indicate that the putative NSCC involved in refilling the sarcoplasmic reticulum (SR) and maintaining the tonic contraction is most likely an SOC-type channel because it appears to be activated by I[P.sub.3]R-channel-mediated SR [Ca.sup.2+] release or store depletion. This is in accordance with its sensitivity to [Ni.sup.2+] and [La.sup.3+] (SOC blockers). More interestingly, RT-PCR analysis indicates that transient receptor potential (Trp1) mRNA is strongly expressed in the rabbit IVC. The Trp1 gene is known to encode a component of the store-operated NSCC. These new data suggest that the activation of both the I[P.sub.3]R channels and the SOC are required for PE-mediated [[[Ca.sup.2+]].sub.i] oscillations and constriction of the rabbit IVC. inosital 1,4,5-trisphosphate; store-operated channels; transient receptor potential gene; vascular smooth muscle

Superficial sarcoplasmic reticulum (SR) regulates smooth muscle force development directly by [Ca.sup.2+] release and removal to and from the cytoplasm (Somlyo and Somlyo. J Cardiovasc Pharmacol 8, Suppl 8: S42-S47, 1986) by buffering [Ca.sup.2+] influx and contributing to [Ca.sup.2+] extrusion (Mueller and van Breemen. Nature 281: 682-683, 1979) and indirectly by releasing [Ca.sup.2+] near [Ca.sup.2+]-activated [K.sup.+] channels ([K.sub.Ca]) to hyperpolarize the plasma membrane (Bolton and Imaizumi. Cell Calcium 20: 141-152, 1996 and Nelson et al. Science 270: 633-637, 1995). In the rabbit basilar artery, relative contributions of direct effects and those mediated through activation of [K.sub.Ca] were evaluated by measuring force and intracellular [Ca.sup.2 +] concentration ([[Ca.sup.2+]][sub.i]) in response to the SR-depleting agents thapsigargin and ryanodine and the large conductance [K.sub.Ca] ([BK.sub.Ca]) blockers iberiotoxin (IbTX) and tetraethylammonium ion (TEA). A large contraction was observed in response to [K.sub.Ca] blockade with either 3 mM TEA or 100 nM IbTX and also after addition of 10 [micro] M ryanodine or 2 [micro] M thapsigargin. When [K.sub.Ca] was blocked first with TEA or IbTX, subsequent addition of thapsigargin or ryanodine also increased force. Measurements of fura 2 fluorescence showed parallel increases in [[Ca.sup.2+]][sub.i] in response to sequential blockade of sarco(endo)plasmic reticulum [Ca.sup.2+]-ATPase and [K.sub.Ca] regardless of the order of application. It appears that a significant fraction of [K.sub.Ca] remains activated in the absence of SR function and that SR contributes to relaxation after blockade of [K.sub.Ca]. We found that depletion of SR before stimulating [Ca.sup.2+] influx through voltage-gated [Ca.sup.2+] channels markedly reduced force development rate and that thapsigargin abolished this effect. We conclude that the SR of rabbit cerebral arteries modulates constriction by direct and indirect mechanisms. cerebral artery; spectrofluorometry; calcium; buffering

Imbalance of signals that control cell survival and death results in pathologies, including cancer and neurodegeneration. Two pathways that are integral to setting the balance between cell survival and cell death are controlled by lipid-activated protein kinase B (PKB)/Akt and Ca2+. PKB elicits its effects through the phosphorylation and inactivation of proapoptotic factors. Ca2+ stimulates many prodeath pathways, among which is mitochondrial permeability transition. We identified Ca2+ release through inositol 1,4,5-trisphosphate receptor (InsP3R) intracellular channels as a prosurvival target of PKB. We demonstrated that in response to survival signals, PKB interacts with and phosphorylates lnsP3Rs, significantly reducing their Ca2+ release activity. Moreover, phosphorylation of lnsP3Rs by PKB reduced cellular sensitivity to apoptotic stimuli through a mechanism that involved diminished Ca2+ flux from the endoplasmic reticulum to the mitochondria. In glioblastoma cells that exhibit hyperactive PKB, the same prosurvival effect of PKB on lnsP3R was found to be responsible for the insensitivity of these cells to apoptotic stimuli. We propose that PKB-mediated abolition of lnsP3-induced Ca2+ release may afford tumor cells a survival advantage. [ABSTRACT FROM AUTHOR]

Endothelin-1 (ET1) is an endogenous vasoconstrictor released by the vascular system to regulate the contractility of vascular smooth muscle cells (VSMC). It is implicated in the pathogenesis of hypertension and diabetic vasculopathy. In rabbit inferior vena cava (IVC), 10 nM ET1 induces tonic contraction mainly via type A endothelin receptor activation. Using confocal imaging of Fluo-3 loaded in thein situ VSMC within the intact IVC, we found that ET1 elicited [Ca2+]i oscillations with an average frequency of 0.31 ± 0.01 Hz. These [Ca2+]i oscillations occurred as repetitive Ca2+ waves traveling along the longitudinal axis of the cells with an average velocity of 29 ± 3 μm/s. The Ca2+ waves were not synchronized between neighboring VSMC nor were they propagated between them. Nifedipine (10 μM) inhibited the tonic contraction by 27.0 ± 5.0% while SKF96365 (50 μM) abolished the remaining contraction. In a parallel Ca2+ study, nifedipine reduced the frequency of the oscillations to 0.22 ± 0.01 Hz while SKF96365 abolished the remaining [Ca2+]i oscillations. Subsequent application of 25 mM caffeine elicited no further Ca2+ signal. Thus, we conclude that ET1 stimulates tonic contraction in the rabbit IVC by inducing [Ca2+]i oscillations and that stimulated Ca2+ entry through both the L-type voltage-gated Ca2+ channels and a nifedipine-resistant and SKF96365-sensitive pathway is crucial for the maintenance of [Ca2+]i oscillations and tonic contraction. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Discusses a study which reported that both the opening of the IP[sub3]R channels and the store operated channels are required for phenylephrine-mediated smooth muscle of the rabbit inferior vena cava. Methodology; Results; Discussion.

We investigated the role of mitochondria (MT) in calcium signaling in a culture of rat aortic smooth muscle cells. We used targeted aequorin to selectively measure [Ca2+] in this organelle. Our results reveal that smooth muscle cell stimulation with agonists causes a large, transient increase in mitochondrial [Ca2+] ([Ca2+]m). This large transient can be blocked with inhibitors of the sarco-endoplasmic reticulum Ca2+-ATPase, suggesting a close relationship between the sarcoplasmic reticulum (SR) and the mitochondria. FCCP completely abolished the response to agonists, and targeted mitochondrial GFP revealed a vast tubular network of MT in these cells. When added before stimulation with ATP, IP3 inhibitors partially blocked the ATP-induced rise in mitochondrial Ca2+ release. The role of the Na+/Ca2+ exchanger (NCX) was examined by removing extracellular Na+. This procedure prevented the decrease in the [Ca2+]m transient normally seen on removal of extracellular Ca2+. We propose a functional linkage of MT and SR dependent on a narrow junctional space between the two organelles in which Ca2+ diffusion is restricted. Approximately half of the mitochondria appear to be associated with the superficial SR, which communicates with the extracellular space via NCX.