American ginseng acutely regulates contractile function of rat heart.

Chronic ginseng treatments have been purported to improve cardiac performance. However reports of acute administration of ginseng on cardiovascular function remain controversial and potential mechanisms are not clear. In this study, we examined the effects of acute North American ginseng (Panax quinquefolius) administration on rat cardiac contractile function by using electrocardiogram (ECG), non-invasive blood pressure (BP) measurement, and Langendorff isolated, spontaneously beating, perfused heart measurements (LP). Eight-week old male Sprague-Dawley rats (n = 8 per group) were gavaged with a single dose of water-soluble American ginseng at 300 mg/kg body weight. Heart rate (HR) and BP were measured prior to and at 1 and 24 h after gavaging (ECG and BP). Additional groups were used for each time point for Langendorff measurements. HR was significantly decreased (ECG: 1 h: 6 ± 0.2%, 24 h: 8 ± 0.3%; BP: 1 h: 8.8 ± 0.2%, 24 h: 13 ± 0.4% and LP: 1 h: 22 ± 0.4%, 24 h: 19 ± 0.4%) in rats treated with water-soluble ginseng compared with pre or control measures. An initial marked decrease in left ventricular developed pressure was observed in LP hearts but BP changes were not observed in BP group. A direct inhibitory effect of North American ginseng was observed on cardiac contractile function in LP rats and on fluorescence measurement of intracellular calcium transient in freshly isolated cardiac myocytes when exposed to ginseng (1 and 10 µg/ml). Collectively these data present evidence of depressed cardiac contractile function by acute administration of North American ginseng in rat. This acute reduction in cardiac contractile function appears to be intrinsic to the myocardium.

The differential regulation of osteoblast and osteoclast activity by surface topography of hydroxyapatite coatings.

The behavior of bone cells is influenced by the surface chemistry and topography of implants and scaffolds. Our purpose was to investigate how the topography of biomimetic hydroxyapatite (HA) coatings influences the attachment and differentiation of osteoblasts, and the resorptive activity of osteoclasts. Using strategies reported previously, we directly controlled the surface topography of HA coatings on polycaprolactone discs. Osteoblasts and osteoclasts were incubated on HA coatings having distinct isotropic topographies with submicrometer and micro-scale features. Osteoblast attachment and differentiation were greater on more complex, micro-rough HA surfaces (Ra ~2 µm) than on smoother topographies (Ra ~1 µm). In contrast, activity of the osteoclast marker tartrate-resistant acid phosphatase was greater on smoother than on micro-rough surfaces. Furthermore, scanning electron microscopy revealed the presence of resorption lacunae exclusively on smoother HA coatings. Inhibition of resorption on micro-rough surfaces was associated with disruption of filamentous actin sealing zones. In conclusion, HA coatings can be prepared with distinct topographies, which differentially regulate responses of osteoblasts, as well as osteoclastic activity and hence susceptibility to resorption. Thus, it may be possible to design HA coatings that induce optimal rates of bone formation and degradation specifically tailored for different applications in orthopedics and dentistry.

Essential role for calcium waves in migration of human vascular smooth muscle cells.

Vascular smooth muscle cell (SMC) migration is characterized by extension of the lamellipodia at the leading edge, lamellipodial attachment to substrate, and release of the rear (uropod) of the cell, all of which enable forward movement. However, little is known regarding the role of intracellular cytosolic Ca(2+) concentration ([Ca(2+)](i)) in coordinating these distinct activities of migrating SMCs. The objective of our study was to determine whether regional changes of Ca(2+) orchestrate the migratory cycle in human vascular SMCs. We carried out Ca(2+) imaging using digital fluorescence microscopy of fura-2 loaded human smooth muscle cells. We found that motile SMCs exhibited Ca(2+) waves that characteristically swept from the rear of polarized cells toward the leading edge. Ca(2+) waves were less evident in nonpolarized, stationary cells, although acute stimulation of these SMCs with the agonists platelet-derived growth factor-BB or histamine could elicit transient rise of [Ca(2+)](i). To investigate a role for Ca(2+) waves in the migratory cycle, we loaded cells with the Ca(2+) chelator BAPTA, which abolished Ca(2+) waves and significantly reduced retraction, supporting a causal role for Ca(2+) in initiation of retraction. However, lamellipod motility was still evident in BAPTA-loaded cells. The incidence of Ca(2+) oscillations was reduced when Ca(2+) release from intracellular stores was disrupted with the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin or by treatment with the inositol 1,4,5-trisphosphate receptor blocker 2-aminoethoxy-diphenyl borate or xestospongin C, implicating Ca(2+) stores in generation of waves. We conclude that Ca(2+) waves are essential for migration of human vascular SMCs and can encode cell polarity.

Calcium sensitization in human esophageal muscle: role for RhoA kinase in maintenance of lower esophageal sphincter tone.

A rise in intracellular-free calcium ([Ca(2+)](i)) concentration is important for initiating contraction of smooth muscles, and Ca(2+) sensitization involving RhoA kinase can sustain tension. We previously found that [Ca(2+)](i) was comparable in cells from the esophageal body (EB) and lower esophageal sphincter (LES) muscles, despite the fact that the LES maintains resting tone. We hypothesized that Ca(2+) sensitization contributes to contraction in human esophageal muscle. Tension and [Ca(2+)](i) were measured simultaneously in intact human EB and LES muscles using the ratiometric Ca(2+)-sensitive dye fura-2. Spontaneous oscillations in EB muscle tension were associated with transient elevations of [Ca(2+)](i). Carbachol caused a large increase in tension, compared with spontaneous oscillations, although the rise of [Ca(2+)](i) was similar, suggesting Ca(2+) sensitization. The RhoA-kinase blockers (R)-(+)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632) and 1-(5-isoquinolinesulfonyl)-homopiperazine hydrochloride (HA-1077) reduced carbachol- and nerve-evoked contraction of the EB, accompanied by smaller reduction in the rise of [Ca(2+)](i). Protein kinase C inhibitors reduced force to a lesser extent. RhoA-kinase blockers caused concentration-dependent reduction of tension in spontaneously contracted LES muscles. Moreover, RhoA-kinase blockers reduced intrinsic nerve-evoked and carbachol-evoked contraction. However, there was no effect on nerve- or nitric oxide-mediated relaxation of LES. Ca(2+) sensitization mediated by the RhoA-kinase pathway has an important role in contraction of human EB muscles and LES tonic contraction, a feature not previously recognized.

Temporal and spatial dynamics underlying capacitative calcium entry in human colonic smooth muscle.

Following smooth muscle excitation and contraction, depletion of intracellular Ca(2+) stores activates capacitative Ca(2+) entry (CCE) to replenish stores and sustain cytoplasmic Ca(2+) (Ca(2+)(i)) elevations. The objectives of the present study were to characterize CCE and the Ca(2+)(i) dynamics underlying human colonic smooth muscle contraction by using tension recordings, fluorescent Ca(2+)-indicator dyes, and patch-clamp electrophysiology. The neurotransmitter acetylcholine (ACh) contracted tissue strips and, in freshly isolated colonic smooth muscle cells (SMCs), caused elevation of Ca(2+)(i) as well as activation of nonselective cation currents. To deplete Ca(2+)(i) stores, the sarcoplasmic reticulum Ca(2+)-ATPase (SERCA) inhibitors thapsigargin and cyclopiazonic acid were added to a Ca(2+)-free bathing solution. Under these conditions, addition of extracellular Ca(2+) (3 mM) elicited increased tension that was inhibited by the cation channel blockers SKF-96365 (10 microM) and lanthanum (100 microM), suggestive of CCE. In a separate series of experiments on isolated SMCs, SERCA inhibition generated a gradual and sustained inward current. When combined with high-speed Ca(2+)-imaging techniques, the CCE-evoked rise of Ca(2+)(i) was associated with inward currents carrying Ca(2+) that were inhibited by SKF-96365. Regional specializations in Ca(2+) influx and handling during CCE were observed. Distinct "hotspot" regions of Ca(2+) rise and plateau were evident in 70% of cells, a feature not previously recognized in smooth muscle. We propose that store-operated Ca(2+) entry occurs in hotspots contributing to localized Ca(2+) elevations in human colonic smooth muscle.

Functional coupling between the Na+/Ca2+ exchanger and nonselective cation channels during histamine stimulation in guinea pig tracheal smooth muscle.

Airway smooth muscle (ASM) contracts partly due to an increase in cytosolic Ca(2+). In this work, we found that the contraction caused by histamine depends on external Na(+), possibly involving nonselective cationic channels (NSCC) and the Na(+)/Ca(2+) exchanger (NCX). We performed various protocols using isometric force measurement of guinea pig tracheal rings stimulated by histamine. We observed that force reached 53 +/- 1% of control during external Na(+) substitution by N-methyl-D-glucamine(+), whereas substitution by Li(+) led to no significant change (91 +/- 1%). Preincubation with KB-R7943 decreased the maximal force developed (52.3 +/- 5.6%), whereas preincubation with nifedipine did not (89.7 +/- 1.8%). Also, application of the nonspecific NCX blocker KB-R7943 and nifedipine on histamine-precontracted tracheal rings reduced force to 1 +/- 3%, significantly different from nifedipine alone (49 +/- 6%). Moreover, nonspecific NSCC inhibitors SKF-96365 and 2-aminoethyldiphenyl borate reduced force to 1 +/- 1% and 19 +/- 7%, respectively. Intracellular Ca(2+) measurements in isolated ASM cells showed that KB-R7943 and SKF-96365 reduced the peak and sustained response to histamine (0.20 +/- 0.1 and 0.19 +/- 0.09 for KB-R, 0.43 +/- 0.16 and 0.47 +/- 0.18 for SKF, expressed as mean of differences). Moreover, Na(+)-free solution only inhibited the sustained response (0.54 +/- 0.25). These data support an important role for NSCC and NCX during histamine stimulation. We speculate that histamine induces Na(+) influx through NSCC that promotes the Ca(2+) entry mode of NCX and Ca(V)1.2 channel activation, thereby causing contraction.

Tachykinin receptor expression and function in human esophageal smooth muscle.

Tachykinins are present in enteric nerves of the gastrointestinal tract and cause contraction of esophageal smooth muscle; however, the mechanisms involved are not understood. Our aim was to characterize tachykinin signaling in human esophageal smooth muscle. We investigated functional effects of tachykinins on human esophageal smooth muscle using tension recordings and isolated cells, receptor expression with reverse transcription (RT)-polymerase chain reaction (PCR) and immunoblotting, intracellular Ca2+ responses using fluorescent indicator dyes, and membrane currents with patch-clamp electrophysiology. The mammalian tachykinins [substance P and neurokinin (NK) A and NKB] elicited concentration-dependent contractions of human esophageal smooth muscle. These responses were not affected by muscarinic receptor or neuronal blockade indicating a direct effect on smooth muscle cells (SMCs). Immunofluorescence and RT-PCR identified tachykinin receptors (NK1, NK2, and NK3) on SMCs. Contraction was mediated through a combination of Ca2+ release from intracellular stores and influx through L-type Ca2+ channels. NK2 receptor blockade inhibited the largest proportion of tachykinin-evoked responses. NKA evoked a nonselective cation current (I(NSC)) with properties similar to that elicited by muscarinic stimulation. The following paradigm is suggested: tachykinin receptor binding to SMCs releases Ca2+ from stores along with activation of I(NSC), which in turn results in membrane depolarization, L-type Ca2+ channel opening, rise of Ca2+ concentration, and contraction. These studies reveal new aspects of tachykinin signaling in human esophageal SMCs. Excitatory tachykinin pathways may represent targets for pharmacological intervention in disorders of esophageal dysmotility.