[Rapid acid extrusion response triggered by alpha-1a adrenoceptor in CHO cells].
Using a microphysiometer with synchronized valve switching, we investigated real-time acid extrusion from CHO cells, in which human alpha-1a adrenoceptor (AR) is stably expressed, in response to noradrenaline (NA). The time course of the extracellular acidification rate after stimulation had two phases: in the first phase, it transiently reached a rate several times greater than the base rate with a peak at around 10 s, and in the second, it reached to 2 times the base rate and reached a plateau in 2 min. Both phases showed concentration-dependent increase of acidification rates in response to NA, but had distinct pEC50 values: 5.6 for the transient phase and 7.2 for the steady phase. HOE642, an inhibitor of Na(+)-H+ exchanger (NHE) 1, inhibited the acid extrusion response in a concentration-dependent manner. HOE642 had high pIC50 values (7.3) for inhibition of the transient phase response. In contrast, it revealed the presence of two components in the steady phase response: one had high pIC50 values (8.2) and the other had low pIC50 values (6.0). As Ca2+ was depleted, the transient phase disappeared, while the steady phase was not affected. These results suggest that alpha-1a AR drives two acid extrusion systems in CHO cells upon stimulation: one elicits the transient response that is largely mediated by a HOE642-sensitive and Ca(2+)-dependent NHE, presumably NHE1, and the other induces the steady acid extrusion that is mediated by NHE1 and another NHE that has low sensitivity to HOE642.
Taniguchi
T
T
Department of Pharmacology, School of Medicine, Fukui Medical University, 23 Shimoaizuki, Matsuoka, Fukui 910-1193, Japan.
D000143:Acids / Q000378:metabolism*; D000818:Animals; D015374:Biosensing Techniques / Q000295:instrumentation*; D016466:CHO Cells / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006146:Guanidines / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009638:Norepinephrine / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000494:pharmacology; D013450:Sulfones / Q000494:pharmacology
D000143:Acids; D006146:Guanidines; D018340:Receptors, Adrenergic, alpha-1; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; C093373:cariporide; D002118:Calcium; D009638:Norepinephrine