SFKs, Ras, and the classic MAPK pathway couple muscarinic receptor activation to increased Na-HCO₃cotransport activity in renal epithelial cells

Abstract

Cholinergic agents are known to affect the epithelial transport of H2O and electrolytes in the kidney. In proximal tubule cells, cholinergic agonists increase basolateral Na-HCO(3) cotransport activity via M(1) muscarinic receptor activation. The signaling intermediates that couple these G protein-coupled receptors to cotransporter activation, however, are not well defined. We therefore sought to identify distal effectors of muscarinic receptor activation that contribute to increased NBC activity in cultured proximal tubule cells. As demonstrated previously for acute CO2-regulated cotransport activity, we found that inhibitors of Src family kinases (SFKs) or the classic mitogen-activated protein kinase (MAPK) pathway prevented the stimulation of NBC activity by carbachol. The ability of carbachol to activate Src, as well as the proximal (Raf) and distal [extracellular signal-regulated kinases 1 and 2 (ERK1/2)] elements of the classic MAPK module, was compatible with these findings. Cholinergic stimulation of ERK1/2 activity was also completely prevented by overexpression of a dominant negative mutant of Ras (N17-Ras). Taken together, these findings suggest a requirement for the sequential activation of SFKs, Ras, and the classic MAPK pathway [Raf-->MAPK/ERK kinase (MEK)-->ERK]. These findings provide important insights into the molecular mechanisms underlying cholinergic regulation of NBC activity in renal epithelial cells. They also suggest a specific mechanism whereby cholinergic stimulation of the kidney can contribute to pH homeostasis.

Effects of chronic treatment with the new ultra‐long‐acting β2‐adrenoceptor agonist indacaterol alone or in combination with the β1‐adrenoceptor blocker metoprolol on cardiac remodelling

“…It has been suggested that desensitization, associated with downregulation of β-adrenoceptors induced by a β-adrenoceptor agonist, is related to the translocation of the β2-adrenoceptor out of caveolae and that this translocation might cause a sequestration of the receptor from the effector, contributing to a reduction in the efficiency of β2-adrenoceptor coupling to AC (Ostrom et al, 2001). Caveolae play a pivotal role in compartmentalizing GRKs, potentially providing a mechanism for rapid activation/inactivation of GRKs that may be necessary in certain signalling situations, such as receptor desentitization (Robey et al, 2001). In addition, indacaterol shows a greater affinity for caveolae and could maintain the efficiency of β-adrenoceptor-linked effectors, reducing desensitization by interacting with caveolae (Lombardi et al, 2009).…”

Regulation of human organic cation transporter hOCT2 by PKA, PI3K, and calmodulin-dependent kinases

“…Wortmannin was able to inhibit tubular basolateral transport of PAH in isolated proximal tubules from rabbit kidney (4) and to inhibit apical P-glycoprotein-mediated drug efflux in the proximal tubule of mice (38). The involvement of G receptor-linked stimulation of MAPK activity was also demonstrated for the regulation of Na-HCO 3 Ϫ cotransport activity after muscarinic stimulation by carbachol in the opossum kidney proximal tubule cell line (28). The components of the signaling pathway of G proteincoupled receptors downstream of PI3K probably have no influence on hOCT2 activity, because inhibition of MEK1 and MEK2 by UO126 had no effect on basal ASP ϩ transport or on carbachol-induced inhibition of ASP ϩ uptake.…”

H2O2-induced Ca2+overload in NRVM involves ERK1/2 MAP kinases: role for an NHE-1-dependent pathway

“…This suggests that ERK1/2 can regulate other ion transporters independently of NHE-1. The possible targets for ERK1/2 that could contribute to the cytosolic Na ϩ and Ca 2ϩ load include the Na ϩ -K ϩ -2Cl Ϫ cotransporter, which is activated by ␣ 1 -adrenergic agonist in an ERK1/2-dependent mechanism in cardiac myocytes (2), or the Na ϩ -HCO 3 Ϫ cotransporter, which is coupled to muscarinic receptor activation by ERK1/2 in renal epithelial cells (30). We cannot rule out the possibility that ERK1/2 can directly modulate NCX or Na ϩ /K ϩ pump activity that could also contribute to alterations in Ca 2ϩ or Na ϩ homeostasis.…”