5-Hydroxytryptamine stimulates net Ca2+ flux in the ventricular muscle of a mollusc (Busycon canaliculatum) during cardioexcitation

Windows to cell function and dysfunction: signatures written in the boundary layers

The medium surrounding cells either in culture or in tissues contains a chemical mix varying with cell state. As solutes move in and out of the cytoplasmic compartment they set up characteristic signatures in the cellular boundary layers. These layers are complex physical and chemical environments the profiles of which reflect cell physiology and provide conduits for intercellular messaging. Here we review some of the most relevant characteristics of the extracellular/intercellular space. Our initial focus is primarily on cultured cells but we extend our consideration to the far more complex environment of tissues, and discuss how chemical signatures in the boundary layer can or may affect cell function. Critical to the entire essay are the methods used, or being developed, to monitor chemical profiles in the boundary layers. We review recent developments in ultramicro electrochemical sensors and tailored optical reporters suitable for the task in hand.

Measuring Ca2+ influxes of TRPC1-dependent Ca2+ channels in HL-7702 cells with non-invasive micro-test technique

AIM

To explore the possibility of using the Non-invasive Micro-test Technique (NMT) to investigate the role of Transient Receptor Potential Canonical 1 (TRPC1) in regulating Ca(2+) influxes in HL-7702 cells, a normal human liver cell line.

METHODS

Net Ca(2+) fluxes were measured with NMT, a technology that can obtain dynamic information of specific/selective ionic/molecular activities on material surfaces, non-invasively. The expression levels of TRPC1 were increased by liposomal transfection, whose effectiveness was evaluated by Western-blotting and single cell reverse transcription-polymerase chain reaction.

RESULTS

Ca(2+) influxes could be elicited by adding 1 mmol/L CaCl(2) to the test solution of HL-7702 cells. They were enhanced by addition of 20 micromol/L noradrenaline and inhibited by 100 micromol/L LaCl(3) (a non-selective Ca(2+) channel blocker); 5 micromol/L nifedipine did not induce any change. Overexpression of TRPC1 caused increased Ca(2+) influx. Five micromoles per liter nifedipine did not inhibit this elevation, whereas 100 micromol/L LaCl(3) did.

CONCLUSION

In HL-7702 cells, there is a type of TRPC1-dependent Ca(2+) channel, which could be detected via NMT and inhibited by La(3+).

Length-dependent deactivation of ventricular trabeculae in the bivalve, Spisula solidissima

Shortening-deactivation has been identified and characterized in ventricular trabeculae of the bivalve, Spisula solidissima (Heterodonta, Mactridae). This muscle had ultrastructural similarities to vertebrate smooth muscle. Deactivation was defined as the fraction of maximal force lost during a contraction when a muscle is shortened rapidly (by a quick-release, QR) to a known length, relative to a control isometric contraction at that same length. The magnitude of deactivation was dependent on the size of the release and the point at which the release was applied during the cycle of contraction. QR/quick-stretch (QS) perturbations at the same point during the contraction resulted in negligible deactivation. The magnitude of deactivation was independent of shortening rate. Deactivation was attenuated by applying caffeine (100 microM) and blocked with high extracellular Ca(2+) (56 mM). The Ca(2+) ionophore, A23187 (10 microM), augmented deactivation as did the positive inotrope serotonin (100 nM). Treatment with ryanodine (5 microM) had no significant effect on deactivation. These results suggest that a reduction in Ca(2+) at the contractile element and/or sequestration of Ca(2+) may occur during shortening. Deactivation may minimize the magnitude of work done during active shortening of bivalve cardiac muscle, particularly against the low afterload exhibited in the bivalve peripheral circulatory system. Intracellular Ca(2+) fluxes during sudden length perturbations may explain the effect of stretch on action potential duration in the bivalve heart, as shown previously.

5-HT induces duodenal mucosal bicarbonate secretion via cAMP- and Ca2+-dependent signaling pathways and 5-HT4 receptors in mice

In previous studies, we have found that 5-hydroxytryptamine (5-HT) is a potent stimulant of duodenal mucosal bicarbonate secretion (DMBS) in mice. The aim of the present study was to determine the intracellular signaling pathways and 5-HT receptor subtypes involved in 5-HT-induced DMBS. Bicarbonate secretion by murine duodenal mucosa was examined in vitro in Ussing chambers. 5-HT receptor involvement in DMBS was inferred from pharmacological studies by using selective 5-HT receptor antagonists and agonists. The expression of 5-HT(4) receptor mRNA in duodenal mucosa and epithelial cells was analyzed by RT-PCR. cAMP-dependent signaling pathway inhibitors MDL-12330A, Rp-cAMP, and H-89 and Ca(2+)-dependent signaling pathway inhibitors verapamil and W-13 markedly reduced 5-HT-stimulated duodenal bicarbonate secretion and short-circuit current (I(sc)), whereas cGMP-dependent signaling pathway inhibitors NS-2028 and KT-5823 failed to alter these responses. Both SB-204070 and high-dose ICS-205930 (selective 5-HT(4) receptor antagonists) markedly inhibited 5-HT-stimulated bicarbonate secretion and I(sc), whereas methiothepine (5-HT(1) receptor antagonist), ketanserin (5-HT(2) receptor antagonist), and a low concentration of ICS-205930 (5-HT(3) receptor antagonist) had no effect. RS-67506 (partial 5-HT(4) receptor agonist) concentration-dependently increased bicarbonate secretion and I(sc), whereas 5-carboxamidotryptamine (5-HT(1) receptor agonist), alpha-methyl-5-HT (5-HT(2) receptor agonist), and phenylbiguanide (5-HT(3) receptor agonist) did not significantly increase bicarbonate secretion or I(sc). RT-PCR analysis confirmed the expression of 5-HT(4) receptor mRNA in murine duodenal mucosa and epithelial cells. These results demonstrate that 5-HT regulates DMBS via both cAMP- and Ca(2+)-dependent signaling pathways and 5-HT(4) receptors located in the duodenal mucosa and/or epithelial cells.