Ca2+ channel subtypes and pharmacology in the kidney

Molecular pharmacology of human Cav3.2 T-type Ca2+ channels: block by antihypertensives, antiarrhythmics, and their analogs

Antihypertensive drugs of the "calcium channel blocker" or "calcium antagonist" class have been used to establish the physiological role of L-type Ca(2+) channels in vascular smooth muscle. In contrast, there has been limited progress on the pharmacology T-type Ca(2+) channels. T-type channels play a role in cardiac pacemaking, aldosterone secretion, and renal hemodynamics, leading to the hypothesis that mixed T- and L-type blockers may have therapeutic advantages over selective L-type blockers. The goal of this study was to identify compounds that block the Ca(v)3.2 T-type channel with high affinity, focusing on two classes of compounds: phenylalkylamines (e.g., mibefradil) and dihydropyridines (e.g., efonidipine). Compounds were tested using a validated Ca(2+) influx assay into a cell line expressing recombinant Ca(v)3.2 channels. This study identified four clinically approved antihypertensive drugs (efonidipine, felodipine, isradipine, and nitrendipine) as potent T-channel blockers (IC(50) < 3 microM). In contrast, other widely prescribed dihydropyridines, such as amlodipine and nifedipine, were 10-fold less potent, making them a more appropriate choice in research studies on the role of L-type currents. In summary, the present results support the notion that many available antihypertensive drugs block a substantial fraction of T-current at therapeutically relevant concentrations, contributing to their mechanism of action.

[Molecular effects of new calcium antagonists: is the principle of parcimony out of place?]

The calcium (Ca2+) channel antagonists (CCA) are used successfully in the treatment of hypertension and angina pectoris. Their mode of action is to decrease Ca2+ entry in the vascular smooth muscle cells. Their molecular targets are voltage activated Ca2+ channels (VACC), especially the L-type (VACC-L). This review examines the role of the VACC-L and of the T-type (VACC-T) in vascular physiology and hypertension. The molecular mechanisms at the base of the vascular selectivity of CCA are presented with, in filigree, the concern of trying to understand the effect of recently developed molecules. In particular, we will examine the ideas having recently emerged concerning the mode of action of last generation dihydropyridines (DHPs) stripped of some of the undesirable effects of prototypes AC considered as highly specific of the VACC-L. These properties could result, in particular, from their effects on the VACC-T, which could occur in addition to those classically observed on the VACC-L.

Calcium, cyclic AMP, and MAP kinases: dysregulation in polycystic kidney disease

Low intracellular calcium, present in untreated polycystic kidney epithelia, results in a proliferative response to cyclic adenosine monophosphate. Treatment with a calcium channel blocker (CCB) caused exacerbation of autosomal dominant polycystic kidney disease in rats. Data regarding use of CCBs in human polycystic kidney disease (PKD) are limited and mixed. Thus, it is premature to extrapolate these findings to human PKD.

T-type calcium channel blockade as a therapeutic strategy against renal injury in rats with subtotal nephrectomy

T-type calcium channel blockers have been previously shown to protect glomeruli from hypertension by regulating renal arteriolar tone. To examine whether blockade of these channels has a role in protection against tubulointerstitial damage, we used a stereo-selective T-type calcium channel blocker R(-)-efonidipine and studied its effect on the progression of this type of renal injury in spontaneously hypertensive rats that had undergone subtotal nephrectomy. Treatment with racemic efonidipine for 7 weeks significantly reduced systolic blood pressure and proteinuria. The R(-)-enantiomer, however, had no effect on blood pressure but significantly reduced proteinuria compared to vehicle-treated rats. Both agents blunted the increase in tubulointerstitial fibrosis, renal expression of alpha-smooth muscle actin and vimentin along with transforming growth factor-beta (TGF-beta)-induced renal Rho-kinase activity seen in the control group. Subtotal nephrectomy enhanced renal T-type calcium channel alpha1G subunit expression mimicked in angiotensin II-stimulated mesangial cells or TGF-beta-stimulated proximal tubular cells. Our study shows that T-type calcium channel blockade has renal protective actions that depend not only on hemodynamic effects but also pertain to Rho-kinase activity, tubulointerstitial fibrosis, and epithelial-mesenchymal transitions.

Cilnidipine and Telmisartan Similarly Improves Vascular Damage in Hypertensive Patients

This study was designed to compare the effects of 12-month blood pressure (BP) control using cilnidipine and telmisartan on vascular damage in untreated hypertensive patients. One hundred patients were randomly assigned to either a cilnidipine group or a telmisartan group. The extent of vascular damage was assessed before and after treatment by measuring urinary albumin excretion (UAE), pulse wave velocity (PWV), and intima-media thickness (IMT) of the carotid arteries in each patient. Both drugs similarly decreased BP without altering plasma markers for oxidative stress or inflammation. Both UAE and PWV were significantly improved in both groups, but IMT was significantly reduced only in the cilnidipine group. Multiple regression analyses suggested that the UAE may have decreased as a result of a reduction in intraglomerular pressure caused by telmisartan or by efferent arteriolar dilation caused by cilnidipine. In addition, the PWV may have decreased as a result of the improvement in lipid metabolism caused by telmisartan or the reduction in plasma levels of aldosterone caused by cilnidipine. However, the analyses could not identify any definitive causal relationships or suggest the mechanism responsible for the improvement in IMT caused by cilnidipine. Thus, telmisartan and cilnidipine have unique properties for inhibiting vascular complications.

Are differences in calcium antagonists relevant across all stages of nephropathy or only proteinuric nephropathy?

PURPOSE OF REVIEW

The main effects of classic calcium antagonists are mediated by the inhibition of L-type calcium channels broadly distributed within the renal vascular bed. Calcium antagonists act predominantly on the afferent arterioles, and dihydropyridines can favour the increase in glomerular hypertension and progression of kidney diseases, in particular when systemic blood pressure remains uncontrolled.

RECENT FINDINGS

Calcium antagonists have been widely used in clinical practice because of their antihypertensive capacity. The prevention of renal damage is a very important aim of antihypertensive therapy. This is particularly so taking into account the high prevalence of chronic kidney disease in the general population. Non-dihydropyridines such as verapamil have been shown to possess an antiproteinuric effect that could be particularly relevant.

SUMMARY

Recent data from clinical trials have confirmed that, in hypertensive patients with preserved renal function or with chronic kidney disease, calcium antagonists are effective antihypertensive drugs to be considered alone or in combination with an angiotensin-converting enzyme inhibitor or an angiotensin receptor blocker. In those patients presenting with proteinuric kidney disease, non-dihydropyridines could reduce proteinuria to a greater degree than dihydropyridines.