Beihua Zhong

N-oleoyldopamine, a novel endogenous capsaicin-like lipid, protects the heart against ischemia-reperfusion injury via activation of TRPV1.

N-oleoyldopamine (OLDA), a bioactive lipid originally found in the mammalian brain, is an endovanilloid that selectively activates the transient receptor potential vanilloid type 1 (TRPV1) channel. This study tests the hypothesis that OLDA protects the heart against ischemia and reperfusion (I/R) injury via activation of the TRPV1 in wild-type (WT) but not in gene-targeted TRPV1-null mutant (TRPV1(-/-)) mice. Hearts of WT or TRPV1(-/-) mice were Langendorffly perfused with OLDA (2 x 10(-9) M) in the presence or absence of CGRP8-37 (1 x 10(-6) M), a selective calcitonin gene-related peptide (CGRP) receptor antagonist; RP-67580 (1 x 10(-6) M), a selective neurokinin-1 receptor antagonist; chelerythrine (5 x 10(-6) M), a selective protein kinase C (PKC) antagonist; or tetrabutylammonium (TBA, 5 x 10(-4) M), a nonselective K(+) channel antagonist, followed by 35 min of global ischemia and 40 min of reperfusion (I/R). Left ventricular end-diastolic pressure (LVEDP), left ventricular developed pressure (LVDP), coronary flow (CF), and left ventricular peak positive dP/dt (+dP/dt) were evaluated after I/R. OLDA improved recovery of cardiac function after I/R in WT but not TRPV1(-/-) hearts by increasing LVDP, CF, and +dP/dt and by decreasing LVEDP. CGRP8-37, RP-67580, chelerythrine, or TBA abolished the protective effect of OLDA in WT hearts. Radioimmunoassay showed that the release of substance P (SP) and CGRP after OLDA treatment was higher in WT than in TRPV1(-/-) hearts, which was blocked by chelerythrine or TBA. Thus OLDA exerts a cardiac protective effect during I/R injury in WT hearts via CGRP and SP release, which is abolished by PKC or K(+) channel antagonists. The protective effect of OLDA is void in TRPV1(-/-) hearts, supporting the notion that TRPV1 mediates OLDA-induced protection against cardiac I/R injury.

Protease-Activated Receptor 2-Mediated Protection of Myocardial Ischemia-Reperfusion Injury: Role of Transient Receptor Potential Vanilloid Receptors

Activation of the protease-activated receptor 2 (PAR2) or the transient receptor potential vanilloid type 1 (TRPV1) channels expressed in cardiac sensory afferents containing calcitonin gene-related peptide (CGRP) and/or substance P (SP) has been proposed to play a protective role in myocardial ischemia-reperfusion (I/R) injury. However, the interaction between PAR2 and TRPV1 is largely unknown. Using gene-targeted TRPV1-null mutant (TRPV1(-/-)) or wild-type (WT) mice, we test the hypothesis that TRPV1 contributes to PAR2-mediated cardiac protection via increasing the release of CGRP and SP. Immunofluorescence labeling showed that TRPV1 coexpressed with PAR2, PKC-epsilon, or PKAc in cardiomyocytes, cardiac blood vessels, and perivascular nerves in WT but not TRPV1(-/-) hearts. WT or TRPV1(-/-) hearts were Langendorff perfused with the selective PAR2 agonist, SLIGRL, in the presence or absence of various antagonists, followed by 35 min of global ischemia and 40 min of reperfusion (I/R). The recovery rate of coronary flow, the maximum rate of left ventricular pressure development, left ventricular end-diastolic pressure, and left ventricular developed pressure were evaluated after I/R. SLIGRL improved the recovery of hemodynamic parameters, decreased lactate dehydrogenase release, and reduced the infarct size in both WT and TRPV1(-/-) hearts (P < 0.05). The protection of SLIGRL was significantly surpassed for WT compared with TRPV1(-/-) hearts (P < 0.05). CGRP(8-37), a selective CGRP receptor antagonist, RP67580, a selective neurokinin-1 receptor antagonist, PKC-epsilon V1-2, a selective PKC-epsilon inhibitor, or H-89, a selective PKA inhibitor, abolished SLIGRL protection by inhibiting the recovery of the rate of coronary flow, maximum rate of left ventricular pressure development, and left ventricular developed pressure, and increasing left ventricular end-diastolic pressure in WT but not TRPV1(-/-) hearts. Radioimmunoassay showed that SLIGRL increased the release of CGRP and SP in WT but not TRPV1(-/-) hearts (P < 0.05), which were prevented by PKC-epsilon V1-2 and H-89. Thus our data show that PAR2 activation improves cardiac recovery after I/R injury in WT and TRPV1(-/-) hearts, with a greater effect in the former, suggesting that PAR2-mediated protection is TRPV1 dependent and independent, and that dysfunctional TRPV1 impairs PAR2 action. PAR2 activation of the PKC-epsilon or PKA pathway stimulates or sensitizes TRPV1 in WT hearts, leading to the release of CGRP and SP that contribute, at least in part, to PAR2-induced cardiac protection against I/R injury.

Cellular biophysical dynamics and ion channel activities detected by AFM-based nanorobotic manipulator in insulinoma β-cells

UNLABELLED Distinct biochemical, electrochemical and electromechanical coupling processes of pancreatic β-cells may well underlie different response patterns of insulin release from glucose and capsaicin stimulation. Intracellular Ca(2+) levels increased rapidly and dose-dependently upon glucose stimulation, accompanied with about threefold rapid increases in cellular stiffness. Subsequently, cellular stiffness diminished rapidly and settled at a value about twofold of the baseline. Capsaicin caused a similar transient increase in intracellular Ca(2+) changes. However, cellular stiffness increased gradually to about twofold until leveling off. The current study characterizes for the first time the biophysical properties underlying glucose-induced biphasic responses of insulin secretion, distinctive from the slow and single-phased stiffness response to capsaicin despite similar changes in intracellular Ca(2+) levels. The integrated AFM nanorobotics and optical investigation enables the fine dissection of mechano-property from ion channel activities in response to specific and non-specific agonist stimulation, providing novel biomechanical markers for the insulin secretion process. FROM THE CLINICAL EDITOR This study characterizes the biophysical properties underlying glucose-induced biphasic responses of insulin secretion. Integrated AFM nanorobotics and optical investigations provided novel biomechanical markers for the insulin secretion process.

Genetic ablation of TRPV1 exacerbates pressure overload-induced cardiac hypertrophy

Transient receptor potential vanilloid 1 (TRPV1) channels expressed in sensory nerves may regulate vascular tone and cardiovascular function via their anti-inflammatory effects by releasing neuropeptide calcitonin gene-related peptide (CGRP). Inflammation plays a role in the progression of cardiac hypertrophy and TRPV1 activation may be key to cardiac inflammatory processes. The aim of this study was to test the hypothesis that TRPV1 modulates inflammatory processes to protect the heart from pressure overload-induced hypertrophy and inflammatory responses. Trpv1 knockout (Trpv1-/-) and wild-type (WT) mice were subjected to transverse aortic constriction (TAC) or sham operation. Four weeks after TAC, WT and Trpv1-/- mice had developed left ventricular (LV) hypertrophy with increased LV mass, fibrosis and infiltration of macrophages as well as increased secretion of tumor necrosis factor α, interleukin-6 from cardiac tissue (all P < 0.05), those were higher in Trpv1-/- than in WT mice with TAC (all P < 0.05). In addition, decreases of LV ejection fraction and fractional shortening were greater in Trpv1-/- than in WT mice (both P < 0.05). Moreover, atrial natriuretic peptide level was greater in Trpv1-/- than in WT mice with TAC (P < 0.05). Compared to sham control, TAC procedure significantly increased cardiac TRPV1 expression and CGRP release in WT mice (both P < 0.05), but not in Trpv1-/- mice. These results demonstrate that Trpv1 gene deletion results in excessive inflammation, exaggerates cardiac hypertrophy, and deteriorates cardiac function after TAC, which may be due to abnormal cardiac remodeling and decreased CGRP in the absence of TRPV1.

Investigations of Bio Markers for ion channel activities on insulinoma cells

Ion channel is the regulatory mechanism for electrical activity in pancreatic islet cells through stimulus-secretion coupling. Changes in membrane potential are regulated by the glucose concentration-dependent ion channel activities. The alteration of glucose concentration is linked to the open probability of ATP-sensitive K+ channels by insulin secretion. At the meantime, the change of glucose concentration can cause the reorganization of the membrane as well as the cytoskeleton, resulting in the change of cellular stiffness. By using an integrated AFM and cell manipulation system, we were able to measure the cell stiffness and structural change simultaneously upon the glucose stimulation. The cell stiffness increases substantially in a dosage-dependent manner after stimulation by real time AFM nanoindentation measurement. Structurally, the cell height decrease dynamically with the glucose concentration increase. Therefore we have a unique Bio Marker to characterize the ion channel activity using different modalities. This result indicates that the open and close of ion channel would lead to the change of membrane structure and thus the cell body exhibits a different cellular stiffness. The study will enhance our understanding of pancreatic islet cell stimulus coupling and insulin secretion.