Characterization of three types of calcium channel in the luminal membrane of the distal nephron

N-/T-Type vs. L-Type Calcium Channel Blocker in Treating Chronic Kidney Disease: A Systematic Review and Meta-Analysis

Renin-angiotensin system (RAS) inhibitors and calcium channel blockers (CCB) are often used together in chronic kidney disease (CKD). The PubMed, EMBASE, and Cochrane Library databases were searched to identify randomized controlled trials (RCTs) in order to explore better subtypes of CCB for the treatment of CKD. This meta-analysis of 12 RCTs with 967 CKD patients who were treated with RAS inhibitors demonstrated that, when compared with L-type CCB, N-/T-type CCB was superior in reducing urine albumin/protein excretion (SMD, −0.41; 95% CI, −0.64 to −0.18; p < 0.001) and aldosterone, without influencing serum creatinine (WMD, −3.64; 95% CI, −11.63 to 4.35; p = 0.37), glomerular filtration rate (SMD, 0.06; 95% CI, −0.13 to 0.25; p = 0.53), and adverse effects (RR, 0.95; 95% CI, 0.35 to 2.58; p = 0.93). In addition, N-/T-type CCB did not decrease the systolic blood pressure (BP) (WMD, 0.17; 95% CI, −1.05 to 1.39; p = 0.79) or diastolic BP (WMD, 0.64; 95% CI, −0.55 to 1.83; p = 0.29) when compared with L-type CCB. In CKD patients treated with RAS inhibitors, N-/T-type CCB is more effective than L-type CCB in reducing urine albumin/protein excretion without increased serum creatinine, decreased glomerular filtration rate, and increased adverse effects. The additional benefit is independent of BP and may be associated with decreased aldosterone (PROSPERO, CRD42020197560).

Calcium channel blocker in patients with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) is involved in a progressive deterioration in renal function over the years and is now a global public health problem. Currently, reducing the number of patients progressing to end-stage renal failure is urgently necessary. Hypertension and CKD interact with each other, and good control of blood pressure (BP) can improve CKD patients' prognosis. With the current global trend for more strict BP control, the importance of BP management and the need for medication to achieve this strict goal are increasing. Calcium channel blockers (CCBs), which target voltage-dependent calcium channels, are frequently used in combination with renin-angiotensin-aldosterone system inhibitors for CKD patients because of their strong BP-lowering properties and relatively few adverse side effects. Calcium channels have several subtypes, including L, N, T, P/Q, and R, and three types of CCBs, L-type CCBs, L-/T-type CCBs, and L-/N-type CCBs, that are available. Nowadays, the new functions and effects of the CCBs are being elucidated.

CONCLUSION

We should use different types of CCBs properly depending on their pharmacological effects, such as the strength of antihypertensive effects and the organ protection effects, taking into account the pathophysiology of the patients. In this article, the role and the use of CCBs in CKD patients are reviewed.

Iron transport in the kidney: implications for physiology and cadmium nephrotoxicity

The kidney has recently emerged as an organ with a significant role in systemic iron (Fe) homeostasis. Substantial amounts of Fe are filtered by the kidney, which have to be reabsorbed to prevent Fe deficiency. Accordingly Fe transporters and receptors for protein-bound Fe are expressed in the nephron that may also function as entry pathways for toxic metals, such as cadmium (Cd), by way of "ionic and molecular mimicry". Similarities, but also differences in handling of Cd by these transport routes offer rationales for the propensity of the kidney to develop Cd toxicity. This critical review provides a comprehensive update on Fe transport by the kidney and its relevance for physiology and Cd nephrotoxicity. Based on quantitative considerations, we have also estimated the in vivo relevance of the described transport pathways for physiology and toxicology. Under physiological conditions all segments of the kidney tubules are likely to utilize Fe for cellular Fe requiring processes for metabolic purposes and also to contribute to reabsorption of free and bound forms of Fe into the circulation. But Cd entering tubule cells disrupts metabolic pathways and is unable to exit. Furthermore, our quantitative analyses contest established models linking chronic Cd nephrotoxicity to proximal tubular uptake of metallothionein-bound Cd. Hence, Fe transport by the kidney may be beneficial by preventing losses from the body. But increased uptake of Fe or Cd that cannot exit tubule cells may lead to kidney injury, and Fe deficiency may facilitate renal Cd uptake.

Calcium-permeable ion channels in the kidney

Calcium ions (Ca(2+)) are crucial for a variety of cellular functions. The extracellular and intracellular Ca(2+) concentrations are thus tightly regulated to maintain Ca(2+) homeostasis. The kidney, one of the major organs of the excretory system, regulates Ca(2+) homeostasis by filtration and reabsorption. Approximately 60% of the Ca(2+) in plasma is filtered, and 99% of that is reabsorbed by the kidney tubules. Ca(2+) is also a critical signaling molecule in kidney development, in all kidney cellular functions, and in the emergence of kidney diseases. Recently, studies using genetic and molecular biological approaches have identified several Ca(2+)-permeable ion channel families as important regulators of Ca(2+) homeostasis in kidney. These ion channel families include transient receptor potential channels (TRP), voltage-gated calcium channels, and others. In this review, we provide a brief and systematic summary of the expression, function, and pathological contribution for each of these Ca(2+)-permeable ion channels. Moreover, we discuss their potential as future therapeutic targets.

Calcium signaling in renal tubular cells

The kidney handles calcium by filtration and reabsorption. About 60% of the plasma calcium is filterable, and 99% is reabsorbed in the tubule. In the proximal tubule, the reabsorption is passive and paracellular, but in the distal tubule is active and transcellular. Thus, renal tubular cells are exposed to very high concentrations of calcium in both, the extracellular and the intracellular compartments. Extracellular calcium signaling is transmitted by the calcium sensing receptor, located both in the luminal and basolateral sides of tubular cells. This receptor is able to control levels of extracellular calcium and acts in consequence to maintain calcium homeostasis. Furthermore, renal tubular cells possess several calcium channels that regulate some of the cell functions. Among those, voltage gated calcium channels, transient receptor potential channels and N-methyl-D-aspartate receptor channels have been reported to control several functions. Those functions include survival, apoptosis, differentiation, epithelial-mesenchymal transition, and active vitamin D and renin synthesis.

Effects of [Ca2+]i and pH on epithelial Na+ channel activity of cultured mouse cortical collecting ducts

[Ca2+]i and pH have been demonstrated to affect Na+ transport in epithelium mediated via the apical epithelial Na+ channel (ENaC). However, it still remains unclear whether the effects of [Ca2+]i and intracellular pH (pHi) on ENaC activity are direct. In this study, inside-out recording was employed to clarify the effects of pH(i) and [Ca2+]i on ENaC activity. We found that elevation of [Ca2+]i induced a significant inhibition of ENaC open probability without altering channel conductance. The inhibitory effect was due to a direct interaction between Ca2+ and ENaC, and is dependent on [Ca2+]i. pHi also directly regulated ENaC open probability. Lower pHi (<7.0) reduced the ENaC open probability as shown in shorter opening time, and higher pH(i) (>7.0) enhanced the ENaC open probability as shown in augmented opening time. pHi did not cause any alteration in channel conductance. The effects of pHi on ENaC open probability could be summarized as an S-shaped curve around pH 7.2.

Ca2+ channel subtypes and pharmacology in the kidney

A large body of evidence has accrued indicating that voltage-gated Ca(2+) channel subtypes, including L-, T-, N-, and P/Q-type, are present within renal vascular and tubular tissues, and the blockade of these Ca(2+) channels produces diverse actions on renal microcirculation. Because nifedipine acts exclusively on L-type Ca(2+) channels, the observation that nifedipine predominantly dilates afferent arterioles implicates intrarenal heterogeneity in the distribution of L-type Ca(2+) channels and suggests that it potentially causes glomerular hypertension. In contrast, recently developed Ca(2+) channel blockers (CCBs), including mibefradil and efonidipine, exert blocking action on L-type and T-type Ca(2+) channels and elicit vasodilation of afferent and efferent arterioles, which suggests the presence of T-type Ca(2+) channels in both arterioles and the distinct impact on intraglomerular pressure. Recently, aldosterone has been established as an aggravating factor in kidney disease, and T-type Ca(2+) channels mediate aldosterone release as well as its effect on renal efferent arteriolar tone. Furthermore, T-type CCBs are reported to exert inhibitory action on inflammatory process and renin secretion. Similarly, N-type Ca(2+) channels are present in nerve terminals, and the inhibition of neurotransmitter release by N-type CCBs (eg, cilnidipine) elicits dilation of afferent and efferent arterioles and reduces glomerular pressure. Collectively, the kidney is endowed with a variety of Ca(2+) channel subtypes, and the inhibition of these channels by their specific CCBs leads to variable impact on renal microcirculation. Furthermore, multifaceted activity of CCBs on T- and N-type Ca(2+) channels may offer additive benefits through nonhemodynamic mechanisms in the progression of chronic kidney disease.