Role of transient receptor potential vanilloid 4 in the effect of osmotic pressure on myocardial contractility in rat / 生理学报

The aim of the present study was to investigate the influence of osmotic pressure on myocardial contractility and the possible mechanism. Electrical stimulation was used to excite papillary muscles of the left ventricle of Sprague-Dawley (SD) rats. The contractilities of myocardium in hyposmotic, isosmotic, and hyperosmotic perfusates were recorded. The influences of agonist and antagonist of the transient receptor potential vanilloid 4 (TRPV4) on the contractility of myocardium under hyposmotic, isosmotic and hyperosmotic conditions were observed. The results were as follows: (1) Compared with that under isosmotic condition (310 mOsm/L), the myocardial contractility was increased by 11.5%, 21.5% and 25.0% (P<0.05) under hyposmotic conditions when the osmotic pressure was at 290, 270 and 230 mOsm/L, respectively; and was decreased by 16.0%, 23.7% and 55.2% (P<0.05) under hyperosmotic conditions when the osmotic pressure was at 350, 370 and 390 mOsm/L, respectively. (2) When ruthenium red (RR), an antagonist of TRPV4, was added to the hyposmotic perfusate (270 mOsm/L), the positive inotropic effect of hyposmia was restrained by 36% (P<0.01); and when RR was added to the hyperosmotic perfusate (390 mOsm/L), the inhibitory effect of hyperosmia on myocardial contractility was increased by 56.1% (P<0.01). (3) When 4-α-phorbol-12,13-didecanoate (4α-PDD), an agonist of TRPV4, was added to the isosmotic perfusate (310 mOsm/L), the myocardial contractility did not change; and when 4α-PDD was added to the hyperosmotic perfusate (390 mOsm/L), the inhibition of myocardial contractility by hyperosmia was increased by 27.1% (P<0.01). These results obtained indicate that TRPV4 is possibly involved in the osmotic pressure-induced inotropic effect.

Decrease of extracellular pH modulates the whole cell voltage-gated potassium currents in rat pulmonary artery smooth muscle cells / 中国应用生理学杂志

<p><b>AIM</b>To study the modulation of extracellular pH on the voltage-gated potassium currents (I(Kv)) in isolated pulmonary artery smooth muscle cells (PASMCs).</p><p><b>METHODS</b>I(Kv) was recorded using whole-cell patch clamp technique under the external solutions with different pH. The electrophysiological characteristics of I(Kv) were then analyzed.</p><p><b>RESULTS</b>(1) As compared to the normoxic group, I(K), decreased under acidic condition. When the extracellular pH were 7.0, 6.5, 6.0, the peak currents at a potential of +60 mV were inhibited by 16.93% +/- 2.47% (P < 0.01), 33.03% +/- 2.13% (P < 0.01), 41.59% +/- 6.53% (P < 0.01) respectively, and the current-voltage relationship (I/V) curve shifted to the right. (2) When the extracellular pH was 7.0, 6.5, 6.0, the voltage-depended Gk-Em was shifted to the direction of positive and the activation was sped up.</p><p><b>CONCLUSION</b>The results suggest that with the development of hypoxic pulmonary vasoconstriction (HPV), extracellular pH may take part in the modulation of Kv channels partly, then make the cell depolarized and decrease the Kv currents, this will lead to open the L-type calcium channel and contract the pulmonary artery smooth muscle. It may be one of the mechanisms that hypoxic leads to HPV and finally accelerate the development of HPV.</p>

Investigation on spontaneous electrical activity of murine embryonic heart using microelectrode arrays / 生理学报

In our studies, we have applied a novel tool, microelectrode arrays (MEA), to investigate the electrophysiological properties of murine embryonic hearts in vitro. The electrical signals were recorded from the areas of the heart adhering to the 60 MEA electrodes, being called field potentials (FPs). As an extracelluar recording, the waveform of the FP appeared similar to a reversed action potential obtained from single cell by whole cell current clamp and the FP duration was comparable with the action potential duration. To study propagation of spontaneous electrical activity, we have compared the occurrence time of FPs recorded from different electrodes. It is shown that there was already an apparent A-V delay [(50.21+/-9.7) ms] at day 9.5 post coitum (E9.5) when heart was still tubular-like and atrium and ventricle were not separated anatomically, while occurence of FP at different electrodes of ventricular area were almost synchronous. Further, we looked into the modulation of spontaneous electrical activity during cardiac development: at E9.5 of embryonic development, 1 mumol/L of isoproterenol (Iso) increased beating frequency by (34.04+/-7.31)%, shortened the A-V delay by (20.00+/-6.44) % and prolonged FP duration. In contrast, 1 mumol/L of carbachol (CCh) slowed down beating frequency by (42.32+/-5.36) %, A-V conduction by (26.00+/-4.81) % and shortened FP duration; however at late stage (E16.5), the regulatory effect of Iso and CCh was strengthened. Therefore we conclude that cardiac conduction system is already established at E9.5 when the four-chambered heart is not formed yet and the regulation of spontaneous activity by sympathetic and para-sympathetic system is gradually matured during cardiac development.