Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The recently cloned rabbit kidney Ca2+-sensing receptor (RabCaR) was functionally characterized in microperfused rabbit cortical thick ascending limb (CTAL) segments. Reverse transcriptase polymerase chain reaction (RT-PCR) confirmed that this nephron segment contains mRNAs coding for the RabCaR. Elevation of the extracellular Ca2+ concentration ([Ca2+]e) from 1 to 5 mmol l-1 induced an increase in the fluorescence emission ratio (R), thus reflecting an increase in intracellular Ca2+ activity ([Ca2+]i). This increase was inhibited by verapamil, nifedipine and SKF 96365, and potentiated by a previous application of Bay K 8644. Neither verapamil nor Bay K 8644 modified the resting [Ca2+]i. This suggests that the basolateral Ca2+ influx induced by a high [Ca2+]e occurs via verapamil- and dihydropyridine-sensitive Ca2+ channels, which are not open under resting conditions. In contrast to that evoked by antidiuretic hormone (ADH), the [Ca2+]i increase induced by a high [Ca2+]e did not result from an accumulation of inositol phosphates. Neomycin, Gd3+, Mg2+, commonly used agonists of the Ca2+-sensing receptor, did not increase the [Ca2+]i. In the presence of verapamil, ADH still produced a transient [Ca2+]i increase that was not observed in the presence of an increased [Ca2+]e. These results suggest that the RabCaR in rabbit CTAL cells is not functionally coupled to phospholipase C. In conclusion, the high [Ca2+]e-induced [Ca2+]i increase involves verapamil- and dihydropyridine-sensitive Ca2+ channels and is independent of phosphoinositide metabolism. Whether these channels are activated by the RabCaR remains to be elucidated.
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PMID:The Ca2+-sensing receptor in the rabbit cortical thick ascending limb (CTAL) is functionally not coupled to phospholipase C. 1008 49

Since extracellular Ca2+ or Mg2+ has been reported to modulate swelling-activated Cl- currents, we examined the expression of the G protein-coupled Ca2+-sensing receptor (CaR) and its involvement in the regulation of volume-sensitive Cl- channels in a human epithelial cell line (Intestine 407). Reverse transcriptase-polymerase chain reaction and immunoblotting analysis showed that Intestine 407 cells express CaR mRNA and protein. The swelling-activated whole-cell Cl- current was voltage-independently augmented by extracellular Ca2+ or Mg2+. In addition, Ca2+ or Mg2+ voltage-dependently accelerated the inactivation kinetics of the Cl- current. Neomycin, spermine and La3+ augmented volume-sensitive Cl- currents. However, these CaR agonists failed to affect depolarization-induced inactivation. Intracellular application of GTPgammaS, but not GDPbeta]S, increased the amplitude of the swelling-induced Cl- current without affecting the basal current. The upregulating effect of Ca2+ on the Cl- current amplitude was abolished by either GTPgammaS or GDPbetaS. In contrast, GTPgammaS and GDPbetaS failed to affect the inactivation kinetics of the Cl- current and the accelerating effect of Ca2+ thereon. The Cl- current amplitude was enlarged by stimulation with forskolin, dibutyryl cAMP and IBMX. During the cAMP stimulation, extracellular Ca2+ failed to increase the Cl- current but did accelerate depolarization-induced inactivation. It is concluded that stimulation of the CaR induces upregulation of volume-sensitive Cl- channels via a G protein-mediated increase in intracellular cAMP in the human epithelial cell. However, the accelerating effect of extracellular divalent cations on the inactivation kinetics of the Cl- current is induced by a mechanism independent of the CaR and cAMP.
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PMID:Ca2+-sensing receptor-mediated regulation of volume-sensitive Cl- channels in human epithelial cells. 1106 Jan 24