Pathophysiological significance of T-type Ca²⁺ channels: Role of T-type Ca²⁺ channels in renal microcirculation

Since conventional Ca²⁺ antagonists, with predominant blockade of L-type voltage-dependent Ca²⁺ channels, elicit preferential dilation of afferent arterioles, they might ostensibly aggravate glomerular hypertension. Recently, novel Ca²⁺ antagonists, with inhibitory action on L-/T-type Ca²⁺ channels, have been reported to dilate both afferent and efferent arterioles. The present review attempted to characterize the renal action of these Ca²⁺ antagonists and evaluated the consequences following the treatment with these agents. In contrast to conventional Ca²⁺ antagonists (e.g., nifedipine), novel antagonists (e.g., benidipine, efonidipine) potently dilated afferent and efferent arterioles; their action on efferent arterioles appeared to be mediated by the T-type Ca²⁺ channel blockade, probably through the inhibition of the intracellular Ca²⁺ release. The comparison of the anti-proteinuric action in subtotally nephrectomized rats showed that efonidipine exerted more prominent action than nifedipine. Furthermore, Ca²⁺ antagonists with T-type Ca²⁺ inhibitory action inhibited renin/aldosterone release and proinflammatory process. Finally, patients with chronic renal disease given a 48-week efonidipine treatment showed reduced proteinuria, and this effect was seen even when mean arterial blood pressure failed to become less than 100 mmHg. Collectively, T-type Ca²⁺ channel blockade provides beneficial action in renal injury. Various mechanisms serve to protect against renal injury, including systemic/glomerular hemodynamic action and non-hemodynamic mechanisms.