Shintaro Yamamoto

TRIC-A Channels in Vascular Smooth Muscle Contribute to Blood Pressure Maintenance.

TRIC channel subtypes, namely TRIC-A and TRIC-B, are intracellular monovalent cation channels postulated to mediate counter-ion movements facilitating physiological Ca(2+) release from internal stores. Tric-a-knockout mice developed hypertension during the daytime due to enhanced myogenic tone in resistance arteries. There are two Ca(2+) release mechanisms in vascular smooth muscle cells (VSMCs); incidental opening of ryanodine receptors (RyRs) generates local Ca(2+) sparks to induce hyperpolarization, while agonist-induced activation of inositol trisphosphate receptors (IP(3)Rs) evokes global Ca(2+) transients causing contraction. Tric-a gene ablation inhibited RyR-mediated hyperpolarization signaling to stimulate voltage-dependent Ca(2+) influx, and adversely enhanced IP(3)R-mediated Ca(2+) transients by overloading Ca(2+) stores in VSMCs. Moreover, association analysis identified single-nucleotide polymorphisms (SNPs) around the human TRIC-A gene that increase hypertension risk and restrict the efficiency of antihypertensive drugs. Therefore, TRIC-A channels contribute to maintaining blood pressure, while TRIC-A SNPs could provide biomarkers for constitutional diagnosis and personalized medical treatment of essential hypertension.

alpha-Adrenoceptor-mediated depletion of phosphatidylinositol 4, 5-bisphosphate inhibits activation of volume-regulated anion channels in mouse ventricular myocytes.

BACKGROUND AND PURPOSE Volume‐regulated anion channels (VRACs) play an important role in cell‐volume regulation. α1‐Adrenoceptor stimulation by phenylephrine (PE) suppressed the hypotonic activation of VRAC current in mouse ventricular cells and regulatory volume decrease (RVD) was also absent in PE‐treated cells. We examined whether the effects of α1‐adrenoceptor stimuli on VRAC current were modulated by phosphatidylinositol signalling.

Reduced volume-regulated outwardly rectifying anion channel activity in ventricular myocyte of type 1 diabetic mice

The currents through the volume-regulated outwardly rectifying anion channel (VRAC) were measured in single ventricular myocytes obtained from streptozotocin (STZ)-induced diabetic mice, using whole-cell voltage-clamp method. In myocytes from STZ-diabetic mice, the density of VRAC current induced by hypotonic perfusion was markedly reduced, compared with that in the cells form normal control mice. Video-image analysis showed that the regulatory volume decrease (RVD), which was seen in normal cells after osmotic swelling, was almost lost in myocytes from STZ-diabetic mice. Some mice were pretreated with 3-O-methylglucose before STZ injection, to prevent the STZ’s β cell toxicity. In the myocytes obtained from such mice, the magnitude of VRAC current and the degree of RVD seen during hypotonic challenge were almost normal. Incubation of the myocytes from STZ-diabetic mice with insulin reversed the attenuation of VRAC current. These findings suggested that the STZ-induced chronic insulin-deficiency was an important causal factor for the attenuation of VRAC current. Intracellular loading of the STZ-diabetic myocytes with phosphatidylinositol 3,4,5-trisphosphate (PIP3), but not phosphatidylinositol 4,5-bisphosphate (PIP2), also reversed the attenuation of VRAC current. Furthermore, treatment of the normal cells with wortmannin, a phosphatidylinositol 3-kinase (PI3K) inhibitor, suppressed the development of VRAC current. We postulate that an impairment PI3K-PIP3 pathway, which may be insulin-dependent, is responsible for the attenuation of VRAC currents in STZ-diabetic myocytes.

α1‐Adrenoceptor‐mediated depletion of phosphatidylinositol 4, 5‐bisphosphate inhibits activation of volume‐regulated anion channels in mouse ventricular myocytes

BACKGROUND AND PURPOSE Volume‐regulated anion channels (VRACs) play an important role in cell‐volume regulation. α1‐Adrenoceptor stimulation by phenylephrine (PE) suppressed the hypotonic activation of VRAC current in mouse ventricular cells and regulatory volume decrease (RVD) was also absent in PE‐treated cells. We examined whether the effects of α1‐adrenoceptor stimuli on VRAC current were modulated by phosphatidylinositol signalling.

Caveolin-3 regulates the Volume-Regulated Anion Channel in Mouse Ventricular Cells

Caveolae are small invaginated microdomains located with a variety of signal transduction molecules on the plasma membrane. Recent reports showed that the knockout mice of a muscle-specific protein caveolin-3 (Cav-3 KO), a principal component of the caveolae in heart, displayed an enlargement of ventricular cells. Volume-regulated outwardly rectifying anion channel (VRAC) is activated by membrane stretch, and play a significant role in cell volume regulation in cardiac cells. However, it is unknown the properties of VRAC in the enlarged cardiac cells from Cav-3 KO mice. In this study, we examined that VRAC current and the cell volume regulation in freshly isolated single ventricular cells from Cav-3 KO mice (Hagiwara et al. 2000). Whole-cell current recording showed that the density of VRAC current induced by extracellular hypotonic solution (HYPO) is markedly reduced in the cells from Cav-3 KO mice, compared to that from wild-type (WT) mice. Video-image analysis revealed that the degree of HYPO-induced cell swelling in Cav-3 KO mice is significantly bigger than that in WT mice, and the regulatory volume decrease, which was seen in WT cells after osmotic swelling, is almost lost in cells from Cav-3 KO mice. This result is in parallel with the VRAC inhibition. In contrast, acidic extracellular pH-activated chloride current and extracellular UTP-activated CFTR current were affected less by the deficiency of caveoline-3. The attenuated VRAC current was restored by intracellular application of a VRAC modulator, phosphatidylinositol 3,4,5-trisphosphate (PIP3). These findings suggested that the attenuation of cardiac VRAC current is due to the PIP3 depletion in Cav-3 KO mice.

α1-Adrenoceptor-mediated depletion of phosphatidylinositol 4, 5-bisphosphate inhibits activation of volume-regulated anion channels in mouse ventricular myocytes: α1-adrenoceptor regulation of chloride channels

BACKGROUND AND PURPOSE Volume‐regulated anion channels (VRACs) play an important role in cell‐volume regulation. α1‐Adrenoceptor stimulation by phenylephrine (PE) suppressed the hypotonic activation of VRAC current in mouse ventricular cells and regulatory volume decrease (RVD) was also absent in PE‐treated cells. We examined whether the effects of α1‐adrenoceptor stimuli on VRAC current were modulated by phosphatidylinositol signalling.