The role of T-type calcium channels in elderly human vascular function: A pilot randomized controlled trial.

Endothelial dysfunction develops with age and may precede cardiovascular disease. Animal data suggest that T-type calcium channels play an important role in endothelial function, but data from humans are lacking. This study included 15 healthy, sedentary, elderly males for a double blinded, randomized controlled trial. For 8 weeks, they were given 40 mg/day of either efonidipine (L- and T-type calcium channel blocker (CCB)) or nifedipine (L-type CCB). Vascular function was evaluated by graded femoral arterial infusions of acetylcholine (ACh; endothelium-dependent vasodilator) and sodium nitroprusside (endothelium-independent vasodilator) both with and without co-infusion of N-acetylcysteine (NAC; antioxidant). We measured leg blood flow and mean arterial pressure and calculated leg vascular conductance to evaluate the leg vascular responses. Despite no significant change in blood pressure in either group, we observed higher leg blood flow responses (Δ 0.43 ± 0.45 l/min, P = 0.006) and leg vascular conductance (Δ 5.38 ± 5.67 ml/min/mmHg, P = 0.005) to intra-arterial ACh after efonidipine, whereas there was no change in the nifedipine group, and no differences between groups. We found no upregulation of endothelial nitric oxide synthase in vastus lateralis muscle biopsies within or between groups. Smooth muscle cell responsiveness was unaltered by efonidipine or nifedipine. Intravenous co-infusion of NAC did not affect endothelium-dependent vasodilatation in either of the CCB groups. These results suggest that 8 weeks' inhibition of T- and L-type calcium channels augments endothelium-dependent vasodilatory function in healthy elderly males. Further studies are required to elucidate if T-type calcium channel inhibition can counteract endothelial dysfunction.

Deficiency of T-type Ca2+ channels Cav3.1 and Cav3.2 has no effect on angiotensin II-induced hypertension but differential effect on plasma aldosterone in mice.

T-type Ca2+ channel Cav3.1 promotes microvessel contraction ex vivo. It was hypothesized that in vivo, functional deletion of Cav3.1, but not Cav3.2, protects mice against angiotensin II (ANG II)-induced hypertension. Mean arterial blood pressure (MAP) and heart rate were measured continuously with chronically indwelling catheters during infusion of ANG II (30 ng·kg-1·min-1, 7 days) in wild-type (WT), Cav3.1-/-, and Cav3.2-/- mice. Plasma aldosterone and renin concentrations were measured by radioimmunoassays. In a separate series, WT mice were infused with ANG II (100 ng·kg-1·min-1) with and without the mineralocorticoid receptor blocker canrenoate. Cav3.1-/- and Cav3.2-/- mice exhibited no baseline difference in MAP compared with WT mice, but day-night variation was blunted in both Cav3.1 and Cav3.2-/- mice. ANG II increased significantly MAP in WT, Cav3.1-/-, and Cav3.2-/- mice with no differences between genotypes. Heart rate was significantly lower in Cav3.1-/- and Cav3.2-/- mice compared with control mice. After ANG II infusion, plasma aldosterone concentration was significantly lower in Cav3.1-/- compared with Cav3.2-/- mice. In response to ANG II, fibrosis was observed in heart sections from both WT and Cav3.1-/- mice and while cardiac atrial natriuretic peptide mRNA was similar, the brain natriuretic peptide mRNA increase was mitigated in Cav3.1-/- mice ANG II at 100 ng/kg yielded elevated pressure and an increased heart weight-to-body weight ratio in WT mice. Cardiac hypertrophy, but not hypertension, was prevented by the mineralocorticoid receptor blocker canrenoate. In conclusion, T-type channels Cav3.1and Cav3.2 do not contribute to baseline blood pressure levels and ANG II-induced hypertension. Cav3.1, but not Cav3.2, contributes to aldosterone secretion. Aldosterone promotes cardiac hypertrophy during hypertension.

Deletion of T-type calcium channels Cav3.1 or Cav3.2 attenuates endothelial dysfunction in aging mice.

Impairment of endothelial function with aging is accompanied by reduced nitric oxide (NO) production. T-type Cav3.1 channels augment nitric oxide and co-localize with eNOS. Therefore, the hypothesis was that T-type channels contribute to the endothelial dysfunction of aging. Endothelial function was determined in mesenteric arteries (perfusion) and aortae (isometric contraction) of young and old wild-type (WT), Cav3.1, and Cav3.2 knockout mice. NO production was measured by fluorescence imaging in mesenteric arteries. With age, endothelium-dependent subsequent dilatation (following depolarization with KCl) of mesenteric arteries was diminished in the arteries of WT mice, unchanged in Cav3.2-/- preparations but increased in those of Cav3.1-/- mice. NO synthase inhibition abolished the subsequent dilatation in mesenteric arteries and acetylcholine-induced relaxations in aortae. NO levels were significantly reduced in mesenteric arteries of old compared to young WT mice. In Cav3.1-/- and Cav3.2-/- preparations, NO levels increased significantly with age. Relaxations to acetylcholine were significantly smaller in the aortae of old compared to young WT mice, while such responses were comparable in preparations of young and old Cav3.1-/- and Cav3.2-/- mice. The expression of Cav3.1 was significantly reduced in aortae from aged compared to young WT mice. The level of phosphorylated eNOS was significantly increased in aortae from aged Cav3.1-/- mice. In conclusion, T-type calcium channel-deficient mice develop less age-dependent endothelial dysfunction. Changes in NO levels are involved in this phenomenon in WT and Cav3.1-/- mice. These findings suggest that T-type channels play an important role in age-induced endothelial dysfunction.

Albuminuria is associated with an increased prostasin in urine while aldosterone has no direct effect on urine and kidney tissue abundance of prostasin.

The proteinase prostasin is a candidate mediator for aldosterone-driven proteolytic activation of the epithelial sodium channel (ENaC). It was hypothesized that the aldosterone-mineralocorticoid receptor (MR) pathway stimulates prostasin abundance in kidney and urine. Prostasin was measured in plasma and urine from type 2 diabetic patients with resistant hypertension (n = 112) randomized to spironolactone/placebo in a clinical trial. Prostasin protein level was assessed by immunoblotting in (1) human and rat urines with/without nephrotic syndrome, (2) human nephrectomy tissue, (3) urine and kidney from aldosterone synthase-deficient (AS-/-) mice and ANGII- and aldosterone-infused mice, and in (4) kidney from adrenalectomized rats. Serum aldosterone concentration related to prostasin concentration in urine but not in plasma. Plasma prostasin concentration increased significantly after spironolactone compared to control. Urinary prostasin and albumin related directly and were reduced by spironolactone. In patients with nephrotic syndrome, urinary prostasin protein was elevated compared to controls. In rat nephrosis, proteinuria coincided with increased urinary prostasin, unchanged kidney tissue prostasin, and decreased plasma prostasin while plasma aldosterone was suppressed. Prostasin protein abundance in human nephrectomy tissue was similar across gender and ANGII inhibition regimens. Prostasin urine abundance was not different in AS-/- and aldosterone-infused mice. Prostasin kidney level was not different from control in adrenalectomized rats and AS-/- mice. We found no evidence for a direct relationship between mineralocorticoid receptor signaling and kidney and urine prostasin abundance. The reduction of urinary prostasin in spironolactone-treated patients is most likely the result of an improved glomerular filtration barrier function and generally reduced proteinuria.

Differential effect of T-type voltage-gated Ca2+ channel disruption on renal plasma flow and glomerular filtration rate in vivo.

Voltage-gated Ca(2+) (Cav) channels play an essential role in the regulation of renal blood flow and glomerular filtration rate (GFR). Because T-type Cav channels are differentially expressed in pre- and postglomerular vessels, it was hypothesized that they impact renal blood flow and GFR differentially. The question was addressed with the use of two T-type Cav knockout (Cav3.1(-/-) and Cav3.2(-/-)) mouse strains. Continuous recordings of blood pressure and heart rate, para-aminohippurate clearance (renal plasma flow), and inulin clearance (GFR) were performed in conscious, chronically catheterized, wild-type (WT) and Cav3.1(-/-) and Cav3.2(-/-) mice. The contractility of afferent and efferent arterioles was determined in isolated perfused blood vessels. Efferent arterioles from Cav3.2(-/-) mice constricted significantly more in response to a depolarization compared with WT mice. GFR was increased in Cav3.2(-/-) mice with no significant changes in renal plasma flow, heart rate, and blood pressure. Cav3.1(-/-) mice had a higher renal plasma flow compared with WT mice, whereas GFR was indistinguishable from WT mice. No difference in the concentration response to K(+) was observed in isolated afferent and efferent arterioles from Cav3.1(-/-) mice compared with WT mice. Heart rate was significantly lower in Cav3.1(-/-) mice compared with WT mice with no difference in blood pressure. T-type antagonists significantly inhibited the constriction of human intrarenal arteries in response to a small depolarization. In conclusion, Cav3.2 channels support dilatation of efferent arterioles and affect GFR, whereas Cav3.1 channels in vivo contribute to renal vascular resistance. It is suggested that endothelial and nerve localization of Cav3.2 and Cav3.1, respectively, may account for the observed effects.

T-type Ca(2+) channels facilitate NO-formation, vasodilatation and NO-mediated modulation of blood pressure.

Voltage-gated calcium channels are involved in the vascular excitation-contraction mechanism and regulation of arterial blood pressure. It was hypothesized that T-type channels promote formation of nitric oxide from the endothelium. The present experiments determine the involvement of T-type channels in depolarization-dependent dilatation of mesenteric arteries and blood pressure regulation in Cav3.1 knock-out mice. Nitric oxide-dependent vasodilatation following depolarization-mediated vasoconstriction was reduced significantly in mesenteric arteries from Cav3.1(-/-) compared to wild type mice. Four days of systemic infusion of a nitric oxide (NO)-synthase-inhibitor to conscious wild type elicited a significant increase in mean arterial blood pressure that was absent in Cav3.1(-/-) mice. Immunoprecipitation and immunofluorescence labeling showed co-localization of Cav3.1 and endothelial nitric oxide synthase (eNOS) in arteries from wild type mice. Nitric oxide release measured as DAF fluorescence and cGMP levels were significantly lower in depolarized Cav3.1(-/-) compared to wild type arteries. In summary, the absence of T-type Cav3.1 channels attenuates NO-dependent dilatation in mesenteric arteries in vitro, as well as the hypertension after L-NAME infusion in vivo. Furthermore, Cav3.1 channels cluster with eNOS and promote formation of nitric oxide by the endothelium. The present findings suggest that this mechanism is important for the systemic impact of NO on peripheral resistance.