MR Spectroscopy in the diagnosis and treatment of breast cancer

In vivo proton magnetic resonance spectroscopy ((1)H MRS) is rapidly becoming useful as a clinical tool for diagnosing and characterizing breast cancers. Alterations of the levels of choline-containing metabolites are associated with malignancy. High-field MR scanners at 1.5 T, 3 T, 4 T, and 7 T have been used to evaluate the role of (1)H MRS measurements of total choline containing compounds in patients with breast cancer. This article will review clinical use of MRI/MRS in vivo. Newer developments in high field MR scanning and quantitative MRS may help breast imagers improve sensitivity and specificity in diagnosing and treating breast cancer.

Upregulation of the T-type calcium current in small rat sensory neurons after chronic constrictive injury of the sciatic nerve

Recent data indicate that peripheral T-type Ca2+ channels are instrumental in supporting acute pain transmission. However, the function of these channels in chronic pain processing is less clear. To address this issue, we studied the expression of T-type Ca2+ currents in small nociceptive dorsal root ganglion (DRG) cells from L4-5 spinal ganglia of adult rats with neuropathic pain due to chronic constrictive injury (CCI) of the sciatic nerve. In control rats, whole cell recordings revealed that T-type currents, measured in 10 mM Ba2+ as a charge carrier, were present in moderate density (20 +/- 2 pA/pF). In rats with CCI, T-type current density (30 +/- 3 pA/pF) was significantly increased, but voltage- and time-dependent activation and inactivation kinetics were not significantly different from those in controls. CCI-induced neuropathy did not significantly change the pharmacological sensitivity of T-type current in these cells to nickel. Collectively, our results indicate that CCI-induced neuropathy significantly increases T-type current expression in small DRG neurons. Our finding that T-type currents are upregulated in a CCI model of peripheral neuropathy and earlier pharmacological and molecular studies suggest that T-type channels may be potentially useful therapeutic targets for the treatment of neuropathic pain associated with partial mechanical injury to the sciatic nerve.

Small-conductance, Ca(2+) -activated K+ channel 2 is the key functional component of SK channels in mouse urinary bladder

Small-conductance Ca(2+)-activated K(+) (SK) channels play an important role in regulating the frequency and in shaping urinary bladder smooth muscle (UBSM) action potentials, thereby modulating contractility. Here we investigated a role for the SK2 member of the SK family (SK1-3) utilizing: 1) mice expressing beta-galactosidase (beta-gal) under the direction of the SK2 promoter (SK2 beta-gal mice) to localize SK2 expression and 2) mice lacking SK2 gene expression (SK2(-/-) mice) to assess SK2 function. In SK2 beta-gal mice, UBSM staining was observed, but staining was undetected in the urothelium. Consistent with this, urothelial SK2 mRNA was determined to be 4% of that in UBSM. Spontaneous phasic contractions in wild-type (SK2(+/+)) UBSM strips were potentiated (259% of control) by the selective SK channel blocker apamin (EC(50) = 0.16 nM), whereas phasic contractions of SK2(-/-) strips were unaffected. Nerve-mediated contractions of SK2(+/+) UBSM strips were also increased by apamin, an effect absent in SK2(-/-) strips. Apamin increased the sensitivity of SK2(+/+) UBSM strips to electrical field stimulation, since pretreatment with apamin decreased the frequency required to reach a 50% maximal contraction (vehicle, 21 +/- 4 Hz, n = 6; apamin, 12 +/- 2 Hz, n = 7; P < 0.05). In contrast, the sensitivity of SK2(-/-) UBSM strips was unaffected by apamin. Here we provide novel insight into the molecular basis of SK channels in the urinary bladder, demonstrating that the SK2 gene is expressed in the bladder and that it is essential for the ability of SK channels to regulate UBSM contractility.

Reducing agents sensitize C-type nociceptors by relieving high-affinity zinc inhibition of T-type calcium channels

Recent studies have demonstrated an important role for T-type Ca2+ channels (T-channels) in controlling the excitability of peripheral pain-sensing neurons (nociceptors). However, the molecular mechanisms underlying the functions of T-channels in nociceptors are poorly understood. Here, we demonstrate that reducing agents as well as endogenous metal chelators sensitize C-type dorsal root ganglion nociceptors by chelating Zn2+ ions off specific extracellular histidine residues on Ca(v)3.2 T-channels, thus relieving tonic channel inhibition, enhancing Ca(v)3.2 currents, and lowering the threshold for nociceptor excitability in vitro and in vivo. Collectively, these findings describe a novel mechanism of nociceptor sensitization and firmly establish reducing agents, as well as Zn2+, Zn2+-chelating amino acids, and Zn2+-chelating proteins as endogenous modulators of Ca(v)3.2 and nociceptor excitability.

Is there a role for T-type calcium channels in peripheral and central pain sensitization?

Following tissue injury, both peripheral and central sensory neurons can become hyperexcitable, or "sensitized." Sensitization can lead to long-term pathological changes in pain sensation. Because many chronic pain conditions are refractory to most currently available treatments, there is great interest in identifying molecular targets that contribute to the sensitization of sensory neurons. Among these, several classes of ion channels have emerged as potential targets. Recent in vitro and in vivo studies have demonstrated a role for T-type Ca2+ channels in sensory pathways and have suggested that these channels may contribute to pain processing and sensitization. Therefore, T-type channels may represent an opportunity for the development of novel pain therapeutics and may help to address an unmet medical need.

Cell-specific alterations of T-type calcium current in painful diabetic neuropathy enhance excitability of sensory neurons

Recent data indicate that T-type Ca2+ channels are amplifiers of peripheral pain signals, but their involvement in disorders of sensory neurons such as those associated with diabetes is poorly understood. To address this issue, we used a combination of behavioral, immunohistological, molecular, and electrophysiological studies in rats with streptozotocin (N-[methylnitrosocarbamoil]-D-glucosamine)-induced early diabetic neuropathy. We found that, in parallel with the development of diabetes-induced pain, T-type current density increased by twofold in medium-size cells from L4-L5 dorsal root ganglia (DRG) with a depolarizing shift in steady-state inactivation. This not only correlated closely with more prominent afterdepolarizing potentials (ADPs) but also increased cellular excitability manifested as a lower threshold for burst firing in diabetic than in control cells. T-type currents and ADPs were potently inhibited by nickel and enhanced by L-cysteine, suggesting that the Ca(V)3.2 T-type channel isoform was upregulated. Both control and diabetic DRG cells with ADPs stained positively for isolectin B4, but only diabetic cells responded robustly to capsaicin, suggesting enhanced nociceptive function. Because increased excitability of sensory neurons may result in such pathological perceptions of pain as hyperalgesia and allodynia, upregulation of T-type Ca2+ currents and enhanced Ca2+ entry into these cells could contribute to the development of symptoms in diabetic neuropathy.

The Role of T-Type Calcium Channels in Epilepsy and Pain

T-type calcium channels open in response to small depolarizations of the plasma membrane. The entry of two positive charges with every calcium ion leads to a further depolarization of the membrane, the low threshold spike, and opening of channels that have a higher threshold. In this manner, T-channels play an important pacemaker role in gating the activity of Na+ and Ca2+ channels. T-channels are preferentially expressed in dendrites, suggesting they play important roles in synaptic integration. Pharmacological evidence indicates that they are expressed in the receptive fields of sensory neurons, suggesting they play a primary role in nociception. Molecular cloning of the three T-channel genes has allowed detailed studies on their channel properties, pharmacology, distribution in the brain, up-regulation in animal models of disease, and provided the tools to screen for novel drugs. Studies on transgenic animals have provided the proof-of-concept that T-channels are important drug targets for the treatment of absence epilepsy and neuropathic pain. Mutations in ion channel genes, or channelopathies, have been found in many diseases. Similarly, T-channel gene mutations have been found in patients with childhood absence epilepsy. Considering the important role T-channels play in the thalamus, it is likely that T-channel mutations also contribute to a wider range of disorders characterized by thalamocortical dysrhythmia.

CaV3.2 is the major molecular substrate for redox regulation of T-type Ca2+ channels in the rat and mouse thalamus

Although T-type Ca(2+) channels in the thalamus play a crucial role in determining neuronal excitability and are involved in sensory processing and pathophysiology of epilepsy, little is known about the molecular mechanisms involved in their regulation. Here, we report that reducing agents, including endogenous sulfur-containing amino acid l-cysteine, selectively enhance native T-type currents in reticular thalamic (nRT) neurons and recombinant Ca(V)3.2 (alpha1H) currents, but not native and recombinant Ca(V)3.1 (alpha1G)- and Ca(V)3.3 (alpha1I)-based currents. Consistent with this data, T-type currents of nRT neurons from transgenic mice lacking Ca(V)3.2 channel expression were not modulated by reducing agents. In contrast, oxidizing agents inhibited all native and recombinant T-type currents non-selectively. Thus, our findings directly demonstrate that Ca(V)3.2 channels are the main molecular substrate for redox regulation of neuronal T-type channels. In addition, because thalamic T-type channels generate low-threshold Ca(2+) spikes that directly correlate with burst firing in these neurons, differential redox regulation of these channels may have an important function in controlling cellular excitability in physiological and pathological conditions and fine-tuning of the flow of sensory information into the central nervous system.

The endogenous redox agent L-cysteine induces T-type Ca2+ channel-dependent sensitization of a novel subpopulation of rat peripheral nociceptors

Recent studies have demonstrated a previously unrecognized contribution of T-type Ca2+ channels in peripheral sensory neurons to pain sensation (nociception). However, the cellular mechanisms underlying the functions of these channels in nociception are not known. Here, in both acutely dissociated and intact rat dorsal root ganglion neurons, we characterize a novel subpopulation of capsaicin- and isolectin B4-positive nociceptors that also expresses a high density of T-type Ca2+ currents. Using these "T-rich" cells as a model, we demonstrate that the endogenous reducing agent L-cysteine lowers the threshold for nociceptor excitability and induces burst firing by increasing the amplitude of T-type currents and shifting the gating parameters of T-type channels. These findings, which provide the first direct evidence of T-type Ca2+ channel involvement in the control of nociceptor excitability, suggest that endogenous T-type channel agonists may sensitize a unique subpopulation of peripheral nociceptors, consequently influencing pain processing under normal or pathological conditions.

Adding in Vivo Quantitative1H MR Spectroscopy to Improve Diagnostic Accuracy of Breast MR Imaging: Preliminary Results of Observer Performance Study at 4.0 T

PURPOSE

To determine whether the addition of in vivo quantitative hydrogen 1 (1H) magnetic resonance (MR) spectroscopy can improve the radiologist's diagnostic accuracy in interpreting breast MR images to distinguish benign from malignant lesions.

MATERIALS AND METHODS

The study was approved by the institutional review board and, where appropriate, was compliant with the Health Insurance Portability and Accountability Act. All patients provided written informed consent. Fifty-five breast MR imaging cases-one lesion each in 55 patients aged 24-66 years with biopsy-confirmed findings-were retrospectively evaluated by four radiologists. Patients were examined with contrast material-enhanced fat-suppressed T1-weighted 4.0-T MR imaging. The concentration of total choline-containing compounds (tCho) was quantified by using single-voxel 1H MR spectroscopy. For each case, the radiologists were asked to give the percentage probability of malignancy, the Breast Imaging and Reporting Data System category, and a recommendation for patient treatment. Two interpretations were performed for each case: The initial interpretation was based on the lesion's morphologic features and time-signal intensity curve, and the second interpretation was based on the lesion's morphologic features, time-signal intensity curve, and tCho concentration. Receiver operating characteristic (ROC), Wilcoxon signed rank, kappa statistic, and accuracy (based on the area under the ROC curve) analyses were performed.

RESULTS

Of the 55 lesions evaluated, 35 were invasive carcinomas and 20 were benign. The addition of 1H MR spectroscopy resulted in higher sensitivity, specificity, accuracy, and interobserver agreement for all four radiologists. More specifically, two of the four radiologists achieved a significant improvement in sensitivity (P=.03, P=.03), and all four radiologists achieved a significant improvement in accuracy (P = .01, P = .05, P = .009, P < .001).

CONCLUSION

Current study results suggest that the addition of quantitative 1H MR spectroscopy to the breast MR imaging examination may help to improve the radiologist's ability to distinguish benign from malignant breast lesions.

Imaging in breast cancer: Magnetic resonance spectroscopy

A technique called in vivo magnetic resonance spectroscopy (MRS) can be performed along with magnetic resonance imaging (MRI) to obtain information about the chemical content of breast lesions. This information can be used for several clinical applications, such as monitoring the response to cancer therapies and improving the accuracy of lesion diagnosis. Initial MRS studies of breast cancer show promising results, and a growing number of research groups are incorporating the technique into their breast MRI protocols. This article introduces 1H-MRS of the breast, reviews the literature, discusses current methods and technical issues, and describes applications for treatment monitoring and lesion diagnosis.

Urodynamic properties and neurotransmitter dependence of urinary bladder contractility in the BK channel deletion model of overactive bladder

Overactive bladder and incontinence are major medical issues, which lack effective therapy. Previously, we showed (Meredith AL, Thornloe KS, Werner ME, Nelson MT, and Aldrich RW. J Biol Chem 279: 36746-36752, 2004) that the gene mSlo1 encodes large-conductance Ca2+-activated K+ (BK) channels of urinary bladder smooth muscle (UBSM) and that ablation of mSlo1 leads to enhanced myogenic and nerve-mediated contractility and increased urination frequency. Here, we examine the in vivo urodynamic consequences and neurotransmitter dependence in the absence of the BK channel. The sensitivity of contractility to nerve stimulation was greatly enhanced in UBSM strips from Slo-/- mice. The stimulation frequency required to obtain a 50% maximal contraction was 8.3 +/- 0.9 and 19.1 +/- 1.8 Hz in Slo-/- and Slo+/+ mice, respectively. This enhancement is at least partially due to alterations in UBSM excitability, as muscarinic-induced Slo-/- contractility is elevated in the absence of neuronal activity. Muscarinic-induced Slo-/- contractility was mimicked by blocking BK channels with iberiotoxin (IBTX) in Slo+/+ strips, whereas IBTX had no effect on Slo-/- strips. IBTX also enhanced purinergic contractions of Slo+/+ UBSM but was without effect on purinergic contractions of Slo-/- strips. In vivo bladder pressure and urine output measurements (cystometry) were performed on conscious, freely moving mice. Slo-/- mice exhibited increased bladder pressures, pronounced pressure oscillations, and urine dripping. Our results indicate that the BK channel in UBSM has a very significant role in urinary function and dysfunction and as such likely represents an important therapeutic target.

Neoadjuvant chemotherapy of locally advanced breast cancer: predicting response with in vivo (1)H MR spectroscopy--a pilot study at 4 T

PURPOSE

To determine if changes in the concentration of choline-containing compounds (tCho) from before primary systemic therapy (PST) to within 24 hours after the first treatment enable prediction of clinical response in patients with locally advanced breast cancer.

MATERIALS AND METHODS

Sixteen women with biopsy-confirmed locally advanced breast cancer scheduled to undergo doxorubicin-based PST were recruited. Magnetic resonance (MR) imaging and spectroscopy were performed at 4 T prior to treatment, within 24 hours after the first dose, and after the fourth dose. Lesion size was assessed by using gadolinium-enhanced MR imaging. Lesion tCho concentration was quantified by using single-voxel hydrogen 1 MR spectroscopy. Statistical analysis was performed by using the Pearson correlation coefficient and the Wilcoxon rank sum test.

RESULTS

Fourteen of 16 patients completed the protocol. In one patient, the level of tCho was not measurable because of unfavorable lesion morphology for MR spectroscopy voxel placement. Of the remaining 13 patients, four had inflammatory breast cancer, six had invasive ductal carcinoma, two had invasive lobular carcinoma, and one had mixed invasive ductal and lobular carcinoma. On the basis of the Response Evaluation Criteria in Solid Tumors, eight of 13 patients had an objective response and five had no response. The change in concentration of tCho from baseline to within 24 hours after the first dose of PST showed significant positive correlation with the change in lesion size (R = 0.79, P = .001). Change in tCho concentration within 24 hours after first dose was significantly different between patients with objective response and those with no response (P = .007).

CONCLUSION

These results suggest that the change in tCho concentration between baseline and 24 hours after the first dose of PST can serve as an indicator for predicting clinical response to doxorubicin-based chemotherapy in locally advanced breast cancer.

Diabetic dyslipidemia and exercise affect coronary tone and differential regulation of conduit and microvessel K+ current

Spontaneous transient outward K(+) currents (STOCs) elicited by Ca(2+) sparks and steady-state K(+) currents modulate vascular reactivity, but effects of artery size, diabetic dyslipidemia, and exercise on these differentially regulated K(+) currents are unclear. We studied the conduit arteries and microvessels of male Yucatan swine assigned to one of three groups for 20 wk: control (C, n = 7), diabetic dyslipidemic (DD, n = 6), or treadmill-trained DD animals (DDX, n = 7). Circumflex artery blood flow velocity obtained with intracoronary Doppler and lumen diameters obtained by intravascular ultrasound enabled calculation of absolute coronary blood flow (CBF). Ca(2+) sparks were determined in pressurized microvessels, and perforated patch clamp assessed K(+) current in smooth muscle cells isolated from conduits and microvessels. Baseline CBF in DD was decreased versus C. In pressurized microvessels, Ca(2+) spark activity was significantly lower in DD versus C and DDX (P < 0.05 vs. DDX). STOCs were pronounced in microvessel (approximately 35 STOCs/min) in sharp contrast to conduit cells ( approximately 2 STOCs/min). STOCs were decreased by 86% in DD versus C and DDX in microvessels; in contrast, there was no difference in STOCs across groups in conduit cells. Steady-state K(+) current in microvessels was decreased in DD and DDX versus C; in contrast, steady-state K(+) current in conduit cells was decreased in DDX versus DD and C. We conclude that steady-state K(+) current and STOCs are differentially regulated in conduit versus microvessels in health and diabetic dyslipidemia. Exercise prevented diabetic dyslipidemia-induced decreases in baseline CBF, possibly via STOC-regulated basal microvascular tone.

Effects of modafinil on wakefulness and executive function in patients with narcolepsy experiencing late-day sleepiness

OBJECTIVES

A modafinil daily dosing strategy promotes wakefulness in narcolepsy patients experiencing excessive daytime sleepiness; however, some patients may continue to experience late-day sleepiness. Excessive sleepiness in narcolepsy is associated with cognitive impairment. Modafinil has improved executive function in other models of excessive sleepiness. This study evaluated the effects of once-daily vs. split doses of modafinil on wakefulness and of combined doses on executive function in narcolepsy patients experiencing late-day sleepiness despite satisfactory modafinil treatment earlier in the day.

METHODS

After a 2-week washout, 24 patients received 3 weeks of double-blind treatment with modafinil 400-mg once daily (7 AM) plus placebo (noon) or modafinil 600-mg split dose (400 mg, 7 AM; 200 mg, noon). Assessments included a Maintenance of Wakefulness Test (MWT) for individual regimens and the Wisconsin Card Sort Test (WCST) for treatments combined.

RESULTS

Modafinil 600-mg split dose was significantly more effective than modafinil 400-mg once daily in improving late-day MWT scores (5 PM-7 PM; P < 0.05). Significant mean (+/- SEM) reductions from baseline of 8.2 +/- 2.7 in the total number of errors and 5.9 +/- 1.9 in total percent of errors (P < 0.05, both) were demonstrated for modafinil on the WCST. Modafinil was well tolerated; adverse events included headache (n = 1), emotional lability (n = 1), bronchitis (n = 1), and accidental injury (n = 2), with no reports of insomnia.

CONCLUSIONS

For patients with residual late-day sleepiness associated with narcolepsy, an additional 200-mg dose of modafinil taken at midday was effective in sustaining wakefulness throughout the entire waking day. Treatment with modafinil also significantly improved executive function.

Novel Ca2+ signalling mechanisms in vascular myocytes: symposium overview

This commentary presents the proceedings of the symposium sponsored by Cardiovascular Section of American Physiological Society in San Diego, CA on 12 April 2003. The major focus of this symposium was on the actions and physiological relevance of several novel Ca2+ signalling mechanisms in vascular smooth muscle (VSM) cells. Five important topics were presented in this symposium including the discovery and roles of cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) in mediating Ca2+ release, Ca2+ sparks and activation of plasma membrane KCa channels in VSM cells, the role of cADPR-mediated activation of ryanodine receptors in the control of vascular tone, the role of [Ca2+]i in mechanotransduction in the arterioles, and interactions of mitochondrial Ca2+ release and SR Ca2+ mobilization. The purpose of this symposium was to promote discussions and exchange of ideas between scientists with interests in Ca2+ signalling mechanisms and those with interests in vascular physiology and pharmacology. The cross-fertilization of ideas is expected to greatly advance our understanding of the physiological and pharmacological relevance of these new Ca2+ signalling mechanisms.

Opposing Effects of Aluminum on Inward-Rectifier Potassium Currents in BeanRoot-Tip Protoplasts

Inward currents in root cap protoplasts of the aluminum-tolerant cultivar, Dade, of Phaseolus vulgaris L. were investigated using the whole-cell patch-clamp technique. The properties of these currents were similar to those seen in inward rectifying K+ channels in other plant tissues. Replacing bath K+ with Na+ nearly abolished the observed currents. Higher bath K+ concentrations increased inward currents. AlCl3 in pH 4.7 bath solutions caused inward K+ currents to activate more rapidly and at more positive voltages when compared with AlCl3 free solutions. In 10 microM AlCl3 the activated inward K+ currents were significantly larger than in the AlCl3-free solution at all voltages except at the most negative voltage of -174 mV and the least negative of -74 mV. In contrast, in 80 microM Al3+, when hyperpolarizing voltages were most negative, the inward K+ currents were inhibited relative to the currents in 10 microM AlCl3. Enhancement of inward K+ currents by AlCl3 is consistent with Al3+ binding to the external surface of the root cap protoplast, decreasing the surface charge, thus causing the channels to sense a more negative membrane potential. Inhibition of inward K+ currents with higher AlCl3 concentrations and more negative voltages is consistent with Al3+ block of K+ channels.

Dosing regimen effects of modafinil for improving daytime wakefulness in patients with narcolepsy

In a multicenter, randomized, double-blind study the authors compared the efficacy of modafinil 400 mg once daily, 400 mg given in a split dose, or 200 mg once daily for maintaining wakefulness throughout the day in patients (N = 32) with narcolepsy reporting a positive daytime response to modafinil but late-afternoon/evening sleepiness. Efficacy evaluations included an extended Maintenance of Wakefulness Test (9:00 am to 9:00 pm), the Clinical Global Impression of Change scale, and the Epworth Sleepiness Scale. Modafinil demonstrated significant improvement in wakefulness as assessed by the Epworth Sleepiness Scale compared with placebo at baseline (all P < 0.001). Modafinil significantly improved patients' ability to sustain wakefulness, as demonstrated by mean sleep latency at week 3 compared with placebo at baseline (all P < 0.001). The 400-mg split-dose regimen improved wakefulness significantly in the evening compared with the 200-mg and 400-mg once-daily regimen (both P < 0.05). The percentage of patients rated as "much improved" or "very much improved" with respect to evening sleepiness was 27%, 82%, and 80% in the 200-mg, 400-mg once-daily, and 400-mg split-dose groups, respectively. Adverse events were mild to moderate in nature and included headache, nausea, nervousness, dyspepsia, pain, and vomiting (all 6%). Some patients may benefit from 400-mg doses of modafinil taken once daily compared with 200-mg doses. A split-dose 400-mg regimen may be superior to once-daily dosing for sustaining wakefulness throughout the entire waking day.

Membrane depolarization, elevated Ca(2+) entry, and gene expression in cerebral arteries of hypertensive rats

Elevated intracellular Ca(2+) ([Ca(2+)](i)) has been implicated in contractile and phenotypic changes in arterial smooth muscle during hypertension. This study examined the role of membrane potential and [Ca(2+)](i) in altered gene expression in cerebral arteries of a rat (Dahl) genetic model of salt-sensitive hypertension. Cerebral arteries from hypertensive animals (Dahl salt-sensitive) exhibited a tonic membrane depolarization of approximately 15 mV compared with normotensive (Dahl salt-resistant) animals. Consistent with this membrane depolarization, voltage-dependent K(+) currents were decreased in cerebral artery myocytes isolated from hypertensive animals. Arterial wall Ca(2+) was elevated in cerebral arteries from hypertensive animals, an effect reversed by diltiazem, a blocker of voltage-dependent Ca(2+) channels. This depolarization-induced increase in [Ca(2+)](i) was associated with increased activation of the transcription factor, cAMP response element binding protein, and increased expression of the immediate early gene c-fos, both of which are reversed by acute exposure to the voltage-dependent Ca(2+) channel blocker nisoldipine. This study provides the first information linking altered Ca(2+) handling to changes in gene expression in cerebral arteries during hypertension.

Beta1-subunit of the Ca2+-activated K+ channel regulates contractile activity of mouse urinary bladder smooth muscle

1. The large-conductance calcium-activated potassium (BK) channel plays an important role in controlling membrane potential and contractility of urinary bladder smooth muscle (UBSM). These channels are composed of a pore-forming alpha-subunit and an accessory, smooth muscle-specific, beta1-subunit. 2. Our aim was to determine the functional role of the beta1-subunit of the BK channel in controlling the contractions of UBSM by using BK channel beta1-subunit 'knock-out' (KO) mice. 3. The beta-galactosidase reporter (lacZ gene) was targeted to the beta1 locus, which provided the opportunity to examine the expression of the beta1-subunit in UBSM. Based on this approach, the beta1-subunit is highly expressed in UBSM. 4. BK channels lacking beta1-subunits have reduced activity, consistent with a shift in BK channel voltage/Ca2+ sensitivity. 5. Iberiotoxin, an inhibitor of BK channels, increased the amplitude and decreased the frequency of phasic contractions of UBSM strips from control mice. 6. The effects of the beta1-subunit deletion on contractions were similar to the effect of iberiotoxin on control mice. The UBSM strips from beta1-subunit KO mice had elevated phasic contraction amplitude and decreased frequency when compared to control UBSM strips. 7. Iberiotoxin increased the amplitude and frequency of phasic contractions, and UBSM tone of UBSM strips from beta1-subunit KO mice, suggesting that BK channels still regulate contractions in the absence of the beta1-subunit. 8. The results indicate that the beta1-subunit, by modulating BK channel activity, plays a significant role in the regulation of phasic contractions of the urinary bladder.

Micromolar Ca(2+) from sparks activates Ca(2+)-sensitive K(+) channels in rat cerebral artery smooth muscle

The goal of the present study was to test the hypothesis that local Ca(2+) release events (Ca(2+) sparks) deliver high local Ca(2+) concentration to activate nearby Ca(2+)-sensitive K(+) (BK) channels in the cell membrane of arterial smooth muscle cells. Ca(2+) sparks and BK channels were examined in isolated myocytes from rat cerebral arteries with laser scanning confocal microscopy and patch-clamp techniques. BK channels had an apparent dissociation constant for Ca(2+) of 19 microM and a Hill coefficient of 2.9 at -40 mV. At near-physiological intracellular Ca(2+) concentration ([Ca(2+)](i); 100 nM) and membrane potential (-40 mV), the open probability of a single BK channel was low (1.2 x 10(-6)). A Ca(2+) spark increased BK channel activity to 18. Assuming that 1-100% of the BK channels are activated by a single Ca(2+) spark, BK channel activity increases 6 x 10(5)-fold to 6 x 10(3)-fold, which corresponds to approximately 30 microM to 4 microM spark Ca(2+) concentration. 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester caused the disappearance of all Ca(2+) sparks while leaving the transient BK currents unchanged. Our results support the idea that Ca(2+) spark sites are in close proximity to the BK channels and that local [Ca(2+)](i) reaches micromolar levels to activate BK channels.

Protein kinases: tuners of the BKCa channel in smooth muscle

Large-conductance, Ca(2+)-activated K(+) (BK(Ca)) channels in smooth muscle cells are unique because they integrate changes in both intracellular Ca(2+) and membrane potential. Protein kinases such as cAMP-dependent protein kinase, cGMP-dependent protein kinase and protein kinase C can affect tissue function by 'tuning' the apparent Ca(2+)- and/or voltage-sensitivity of the BK(Ca) channel to physiological changes in both Ca(2+) concentrations and membrane potential. However, despite the central importance of kinase-mediated modulation of BK(Ca) channels in different smooth muscle tissues, many key issues, including the sites and mechanisms of actions of protein kinases, remain unresolved. In this article, the role of protein kinases in the regulation of BK(Ca) channels is discussed.